effect of loi of fly ash on properties of...

EFFECT OF LOI OF FLY ASH ON PROPERTIES

OF CONCRETE

BY

YOUPHALAT PHETHANY

A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE

REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE

(ENGINEERING AND TECHNOLOGY)

SIRINDHORN INTERNATIONAL INSTITUTE OF TECHNOLOGY

THAMMASAT UNIVERSITY

ACADEMIC YEAR 2017

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Acknowledgements

The author would like to express his deepest gratitude to his advisor Dr.

Parnthep Julnipitawong for his continuously invaluable guidance and advice through

the duration of this thesis.

Sincere gratitude is also extended to his thesis committee members Prof. Dr.

Somnuk Tangtermsirikul, Dr Krittiya Kaewmanee for their valuable comments and

guidance on my thesis. A special thank is conveyed to Asst. Prof Dr Pitisan Krammart

of Rajamangala University of Technology Thanyaburi for serving as an external

examiner for this thesis. Another special thank is conveyed to Asst. Prof. Dr

Warakana Saengsoy and Dr. Lalita Yongchaitrakul for their memorable and valuable

advice.

Grateful acknowledgements are conveyed to AUN-seednet and Sirindhorn

International Institute of Technology (SIIT) for providing him the scholarship for

master degree at Sirindhorn International Institute of Technology, Thammasat

University.

The author also wishes to show his gratitude to his colleagues, senior project

students and laboratory technician for their assistance, support, advice and humor

during the laboratory and hismaster student life.

Special thanks are given to all staff of Sirindhorn International Institute of

Technology for their kind services and information throughout his study.

Finally and most importantly, he sincerely and gratefully dedicates this work

to his beloved family for their tremendous encouragement and constant support to his

study and all his life. He specially wants to thank his parents for their incomparable

love, sacrifices and patience.

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Abstract

EFFECT OF LOI OF FLY ASH ON PROPERTIES OF CONCRETE

by

YOUPHALAT PHETHANY

Bachelor of Engineering (Civil Engineering), National University of Laos, Laos, 2014

Master of Science (Engineering and Technology), Sirindhorn International Institute of

Technology, Thammasat University, Thailand, 2018

The quantity of low LOI fly ash available is decreasing worldwide as an

indirect result of controlling toxic gases such as nitrogen oxides (NOx) to meet the

emission standards of the 1990 Clean Air Act amendments. More recent coal power

plants around the world are equipped with low NOx burners in their boilers, which are

operated at lower firing temperature. This approach has an adverse effect on the

quality of fly ash produced because it increases the %LOI of the produced fly ash.

The term LOI basically stands for Loss on Ignition. Generally, the amount of

unburned carbon of fly ash can be easily determined by the LOI test (ASTM D7348).

High LOI fly ash is generally known to cause some malfunctions in concrete, which

are probably known to include discoloration, poor air entrainment ability, high water

requirement and low compressive strength. Therefore it was only utilized in low-

value method or disposed at landfills. So, to utilize these high LOI fly ashes in the

concrete work, which is the high-value application for fly ash, the unburned carbon

needs to be reduced either by optimizing combustion process or by efficient carbon

separation techniques. However, both the disposal and the carbon reduction processes

of fly ash are complicated and required large budget and time in the process.

Therefore, better understanding of high LOI fly ash concrete behavior is crucial to be

capable of using it directly in concrete work without needs of additional process.

This research aims to investigate and clarify the effect of LOI of fly ash on

many basic properties and durability of concrete. To be able to compare the

performances of fly ash concrete containing various %LOI and to vary the %LOI of

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fly ash without any changes in chemical and physical properties, artificial high LOI

fly ashes were made and used throughout this entire study. Low LOI fly ash, having

%LOI of 0.77% from Mae-Moh power plant, Thailand, and powder activated carbon

were used to make other 4 artificial high LOI fly ashes, having %LOI of 6%, 12%,

18% and 25%. Two replacement percentages of fly ash were used at 20% and 40%.

Two different curing conditions, which are air curing and water curing, were used to

investigate the curing sensitivity of high LOI fly ash concrete. Basic properties of low

and high LOI fly ashes such as moisture content, specific gravity, Blaine fineness,

water retainability and water requirement were preliminarily investigated. After that,

experiments on the slump, compressive strength, shrinkage, carbonation and chloride

resistance were carried out. Moreover, slump model and investigation on the

microstructure of low and high LOI fly ash concrete were done for clarifying the test

results.

Moisture content of fly ash increases with the increase of its %LOI. However, the

moisture content of fly ash having %LOI of 25% is still lower than the limit in ASTM

standard specification, which limits the maximum moisture content of fly ash used in

concrete at 3%. Particle size distributions of the prepared high LOI fly ashes are

coarser than the low LOI fly ashes, whereas the Blaine fineness of high LOI fly ashes

are higher. This is because high LOI fly ashes used in this study have more porous

structure and contain irregular particles, because of the added PAC particles. Water

retainability of fly ash increases when %LOI of fly ash increases due to the porous

and rough-texture particles. Therefore, high LOI fly ashes increase the water

requirement of the mixtures.

Using low LOI fly ash significantly improves the slump of concrete compared to

the cement-only mixture. However, slump of fly ash concrete was significantly

affected by the %LOI of fly ash. The initial slump of concrete gradually decreases

with the increase of %LOI of fly ash. Nevertheless, using fly ash having %LOI of

0.77% to 6% with replacement percentage of 20% in the mixture seems to improve

the workability of concrete comparing to the cement-only mixture. Increase percent

replacement of fly ash from 20% to 40% significantly enhances slump of fly ash

concrete having %LOI of 0 to 12%. On the contrary, the slump of concrete with 40%

fly ash replacement gradually decreases and becomes worse than that of 20%

replacement when %LOI of fly ash is over 12%. This phenomenon is because when

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the high amount of high LOI fly ash is used in the mixture, its water retainability

plays the more important role than its lubrication effect.

The reduction in compressive strength of high LOI fly ash concrete was obtained

in the case of the controlled slump by adjustment of water. However, the increase in

compressive strength of high LOI fly ash concrete was obtained in the cases of the

controlled slump by the use of superplasticizer and controlled w/b. In the latter 2

cases, the compressive strength of concrete gradually increases when %LOI of fly ash

increases from 0.77 to 12%. Although the compressive strength tends to gradually

decrease when %LOI of fly ash is beyond 12%, the overall compressive strength of

high LOI fly ash concrete is comparable to fly ash concrete with the lowest %LOI

(LOI=0.77%). Increase the replacement percentage of fly ash from 20% to 40%

resulted in lower compressive strength for mixtures with fly ash with all %LOI. Using

high LOI fly ashes in the mixtures can reduce the curing sensitivity of fly ash

concrete, especially the one that containing %LOI of 12% due to its internal curing

effect. The increase in compressive strength of high LOI fly ash concrete was found

to be due to its internal curing effect. SEM pictures of polished high LOI fly ash

concrete showed that cement paste infiltrated into the rough surface and pores of the

carbon particles. Cement and fly ash react with the additional water, absorbed by the

carbon particles, resulting in better bonding between cement and carbon particles.

Moreover, the result from micro hardness test of high LOI fly ash concrete also

revealed that the hardness values near to carbon particles were higher than those near

to fly ash particles, proofing the existence of hard shell around the carbon particles.

Carbonation and chloride resistances of high LOI fly ash concrete are worse than

the low LOI fly ash concrete. However, the effect of LOI of fly ash was less

significant when using in low w/b concrete. Autogenous shrinkage of high LOI fly

ash was significantly decreased. This result is one of the evidences indicating the

internal curing ability of high LOI fly ash. Total shrinakge of high LOI fly ash

concrete gradually increases with the increase of %LOI of fly ash. However, the use

of fly ash with %LOI of 0.77 to 25% can reduce the total shrinkage when compared to

the OPC mixture.

Keywords: High LOI fly ash, fly ash, water retainability, compressive strength,

curing sensitivity, carbonation, shrinkage

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Table of Contents

Chapter Title Page

Signature Page i

Acknowledgements ii

Abstract iii

Table of Contents vi

List of Figures x

List of Tables xiii

1 Introduction 1

1.1 General 1

1.2 Statement of problems 2

1.3 Objectives 3

1.4 Scope of study 4

2 Literature Review 5

2.1 Fly ash 5

2.1.1 Chemical composition and mineralogical of fly ash 6

2.1.2 Physical properties and morphology of fly ash 7

2.1.3 High LOI fly ash 9

2.2 Standard specifications of fly ash for use in concrete 10

2.2.1 ASTM standard 10

2.2.2 Vietnamese standard 11

2.2.3 Thai standard 13

2.2.4 Japanese standard 13

2.3 Effect of fly ash on concrete properties 14

2.3.1 Effect of fly ash on properties of fresh concrete 14

2.3.2 Effect of fly ash on compressive strength of concrete 16

2.3.3 Effect of fly ash on durability of concrete 19

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3 Experimental Program 22

3.1 General 22

3.2 Materials 22

3.2.1 Cement 22

3.2.2 Fly ashes 22

3.2.3 Activated carbon 24

3.3 PAC selection and preparation 25

3.4 Experimental Methodology 28

3.4.1 Properties of artificial high LOI fly ash 28

3.4.1.1 Loss on ignition 28

3.4.1.2 Water retainability 30

3.4.2 Basic and mechanical properties of high LOI fly ash concrete 31

3.4.2.1 Slump 31

3.4.2.2 Compressive strength 33

3.4.3 Durability 36

3.4.3.1 Autogenous shrinkage 36

3.4.3.2 Total shrinkage 38

3.4.3.3 Carbonation 39

3.4.3.4 Rapid Chloride Penetration Test (RCPT) 41

3.4.4 Microstructure of high LOI fly ash concrete 44

3.4.4.1 Porosity of concrete 44

3.4.4.2 Micro hardness 44

4 Results of Basic Properties of High LOI Fly Ash 47

4.1 General 47

4.2 Morphology of fly ashes and powdered activated carbons 47

(PACs)

4.2.1 Morphology of fly ashes with various %LOI 47

4.2.2 Morphology of powdered activated carbons (PACs) 51

4.3 Properties of artificial high LOI fly ash 53

4.3.1 Basic properties of fly ash 55

4.3.2 Particle size distribution 56

4.3.3 Water retainability 57

4.3.4 Water requirement 58

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5 Results and Clarifications of Slump 59

5.1 Initial slump of concrete 59

5.2 Clarification of slump behavior 61

5.2.1 Background of slump model 61

5.2.1.1 Slope of slump-free water content curve (α) 61

5.2.1.2 Free water content in fresh concrete (Wfr) 62

(1) Water retainability of powder materials (β𝑝) 62

(2) Surface water retainability of aggregates (Wra′ ) 63

(a) Water retainability coefficient of aggregates 63

(βagg′)

(b) Determination of specific surface area of fine 63

and coarse aggregate

5.2.1.3 Minimum free water content required to initiate slump 64

(W0)

(1) Effective surface area of solid particles (Seff) 65

(2) Lubrication coefficient (L) 66

5.2.2 Verification of initial slump of high LOI fly ash concrete 66

6 Results and Clarifications of Compressive Strength 72

6.1 General 72

6.2 Effect of high LOI fly ash on compressive strength of concrete 72

6.2.1 Controlled slump 72

6.2.2 Controlled water to binder ratio 74

6.3 Effect of fly ash content on compressive strength of high LOI 76

fly ash concrete

6.4 Effect of different curing conditions on compressive strength 79

of high LOI fly ash concrete

6.4.1 Controlled water to binder 79

6.4.2 Controlled slump by using superplasticizer 80

6.5 Curing sensitivity of high LOI fly ash concrete on compressive 81

strength

6.6 Microstructure study of high LOI fly ash concrete 83

6.6.1 Porosity of fly ash mortars and concrete with different %LOI 83

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6.6.2 Microstructure examination of high LOI fly ash concrete 85

by SEM

6.6.3 Experiment on micro hardness 88

7 Results of Durability of High LOI Fly Ash Concrete 92

7.1 Effect of high LOI fly ash on carbonation resistance 92

7.2 Effect of high LOI fly ash on chloride resistance 97

7.3 Effect of high LOI fly ash on shrinkage 99

7.3.1 Autogenous shrinkage 99

7.3.2 Total shrinkage 100

8 Conclusions and Recommendations 102

8.1 Conclusions 102

8.2 Recommendations for future studies 105

References 106

Appendices 113

Appendix A 114

Appendix B 116

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List of Figures

Figures Page

2.1 Survey of products containing SiO2, Al2O3 and CaO 6

2.2 Backscattered electron (BSE) images of different fly ash particles 8

2.3 SEM images of unburned carbon particles 10

2.4 Reduction of water demand of fresh concrete with a spread of 42 cm 15

3.1 Fly ash from different sources 23

3.2 Particle shapes of activated carbon (AC) from different sources 24

3.3 Planetary ball mill 26

3.4 Grinding process of powdered activated carbon (PAC) 26

3.5 Schematic outline of this study 27

3.6 Apparatus for LOI test 29

3.7 Mini slump test 30

3.8 Mixture designation nomenclature 31

3.9 Apparatus for slump test 32

3.10 Cube molds having size of 10x10x10 cm for casting concrete 34

3.11 Compressive strength test machine 34

3.12 Bar molds for autogenous and total shrinkage test 36

3.13 Autogenous shrinkage paste specimens 37

3.14 The length comparator used for measuring expansion of 37

the bar specimens

3.15 Bar specimens for total shrinkage test 38

3.16 Specimens after spraying phenolphthalein solution 40

3.17 Cylinder molds 41

3.18 A slice of RCPT specimen 42

3.19 Apparatus for Rapid Chloride Penetration Test 42

3.20 Mold and cube concrete specimens 45

3.21 Concrete cubes inside resin after polishing 45

3.22 Vickers hardness test apparatus 46

4.1 SEM pictures of low LOI fly ash (LOI = 0.77%) 48

from Mae-Moh power station, Thailand

4.2 SEM pictures of high LOI fly ash (LOI = 5.36%) 49

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from BLCP power station, Thailand

4.3 SEM pictures of high LOI fly ash (LOI=18.04%) from Vietnam 50

4.4 EDX result of particle #1, Vietnamese fly ash 51

4.5 SEM pictures of Powdered Activated Carbons (PACs) 52

4.6 Particle size distributions of UC-FV and PAC-BC 53

4.7 SEM pictures of real and artificial high LOI fly ashes 54

4.8 Particle size distributions of cement, fly ashes with various 56

%LOI and PAC produced from bituminous coal

4.9 Water retainability coefficients of fly ashes with various %LOI 57

4.10 Water requirement of mortars containing fly ashes with various %LOI 58

5.1 Initial slump of concrete containing fly ashes with various %LOI 60

(w/b=0.4)

5.2 Initial slump of concrete containing fly ashes with various %LOI 60

(w/b =0.5)

5.3 Predicted slump of low and high LOI fly ash concrete (w/b =0.4) 69

5.4 Predicted slump of low and high LOI fly ash concrete (w/b =0.5) 69

5.5 Water retainability coefficients of fly ashes at with various %LOI 70

5.6 Lubrication coefficient of fly ashes with various %LOI 70

5.7 Relationship between Wfr, W0 and %LOI of fly ash (w/b =0.4) 71

6.1 Compressive strength of OPC and fly ash concrete, containing various 73

%LOI (controlled slump by adjustment of water)


%LOI (controlled slump by using superplasticizer)


%LOI (20% fly ash replacement, controlled w/b at 0.4)



6.5 Compressive strength of high LOI fly ash concrete with various 77

%replacements of 20 and 40% (w/b =0.4)

6.6 Compressive strength of high LOI fly ash concrete with various 78

%replacements of 20 and 40% (w/b =0.5)

6.7 Compressive strength of high LOI fly ash concrete in 79

different curing conditions (controlled w/b at 0.4)

6.8 Compressive strength of high LOI fly ash concrete in 80

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different curing conditions (controlled slump by using superplasticizer)

6.9 Curing sensitivity of fly ash concrete containing various %LOI 82

for controlled w/b case (w/b=0.4)

6.10 Curing sensitivity of fly ash concrete containing various %LOI 83

for controlled slump at 8.5 cm by using admixture case

6.11 Total volume of permeable voids in fly ash mortars with different %LOI 84

6.12 Total volume of permeable voids in fly ash concrete with different %LOI 84

6.13 ITZ microstructure of high-carbon fly ash lightweight aggregate concrete 86

6.14 Typical view of paste around a particle of fly ash and carbon 87

6.15 ITZ microstructure of a carbon particle and cement paste 87

6.16 Average hardness values near to fly ash particles with their 89

tested locations of concrete containing fly ash with %LOI 0.77%

6.17 Average hardness values near to carbon particles with their 90

tested locations of concrete containing fly ash with %LOI 12%

6.18 Average hardness values near to fly ash particles with their 91

tested locations of concrete containing fly ash with %LOI 12%

7.1 Carbonation depth of fly ash concrete containing various %LOI 93

at different exposure periods, (water-cured condition)

7.2 Carbonation depth of fly ash concrete containing various %LOI 94

at different exposure periods, (water-cured and air-cured condition)

7.3 Curing sensitivity index on carbonation of fly ash concrete 96

containing various %LOI (w/b=0.4), at different exposure periods

7.4 Chloride permissibility of fly ash concrete containing various %LOI 98

by measuring charge passed (w/b=0.4)

7.5 Chloride permissibility of fly ash concrete containing various %LOI 98

by measuring charge passed (w/b=0.5)

7.6 Autogenous shrinkage of pastes containing fly ashes with various %LOI 99

(w/b=0.25)

7.7 Autogenous shrinkage of pastes containing fly ashes with various %LOI 100

(w/b=0.40)

7.8 Total shrinkage of pastes containing fly ashes with various %LOI 101

(w/b=0.25)

7.9 Total shrinkage of pastes containing fly ashes with various %LOI 101

(w/b=0.40)

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List of Tables

Tables Page

1.1 Summary of maximum allowable %LOI of fly ash for use in 3

cement/concrete in different coal-using countries

2.1 Chemical properties requirements for fly ash use as mineral admixtures 11

in Porland cement concrete according to ASTM C618

2.2 Specifications of fly ash for concrete and mortar according to 12

TCVN 10302:2013

2.3 Chemical properties, specification of fly ash according to TIS 2135 13

2.4 Standard specifications of fly ash according to JIS-A 6201-1999 14

3.1 Chemical compositions of cement and fly ash 23

3.2 Physical properties of cement and fly ash 23

3.3 Chemical compositions of powdered activated carbons (PACs) 24

3.4 Mix proportions of concrete for slump test. 32

3.5 Mix proportions of concrete for compressive strength test. 35

3.6 Mix proportions of pastes for autogenous shrinkage and total shrinkage 39

test

3.7 Mix proportions of concrete for carbonation and RCPT test 43

4.1 Actual tested %LOI in the prepared fly ashes 55

4.2 Moisture content, specific gravity and Blaine fineness of fly ashes with 55

various %LOI

5.1 Tested and predicted slump results of fly ash concrete containing 67

various %LOI (w/b =0.4)

5.2 Tested and predicted slump results of fly ash concrete containing 67

various %LOI (w/b =0.5)

6.1 Hardness values near fly ash particles of W40FM0 mixture 89

6.2 Hardness values near carbon particles of W40FM12 mixture 90

6.3 Hardness values near fly ash particles of W40FM12 mixture 91

8.1 Performances of high LOI fly ash compared with low LOI fly ash 102

8.2 Performances of high LOI fly ash mixture compared with 103

cement-only mixture

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Chapter 1

Introduction

1.1 General

At present, fly ash, a by-product from the combustion of pulverized coal in

electricity generating power plant, is increasingly utilized worldwide as a cement

replacement material in concrete industry due to its merits in the sense of improving

many concrete properties, cost reduction of concrete and also reducing environmental

problems. The use of good quality fly ash with optimum amount to partially replacing

cement improves many properties of concrete i.e. increasing workability and

pumpability of fresh concrete, improving long-term compressive strength, reducing

temperature, reducing shrinkage, improving resistance against chloride-induced steel

corrosion, increasing sulfate resistance, reducing risk due to alkali-aggregate reaction,

etc [1-7].

Chemical and physical properties of fly ash vary and depend on type of coal,

fineness of pulverized coal, characteristics of furnace, burning and collecting process,

etc. The variation and inconsistency of its properties are the main issues for utilization

of fly ash in concrete works. To ensure that fly ashes are suitable for use in concrete

works, standard specifications (ASTM [8], TIS [9], JIS [10], TCVN [11], etc) have

been drafted in many countries for their local fly ashes based on chemical

composition, physical properties which includes Loss on Ignition (LOI) percentage.

The %LOI of fly ash represents its approximated amount of unburned carbon content.

The excessive amount of sulfur, freelime and unburned carbon content of fly ash

could adversely affect some of the properties of fly ash concrete [12-14].

Thailand is one of the countries that has been very successful in regard to fly

ash usage in concrete industry. The sources of utilized fly ash in Thailand are from

two major locations, which are Lampang (Mae-Moh) and Rayong (BLCP). Mae-Moh

fly ash has low SiO2 content, but high in CaO which contributes to the high

compressive strength of Mae-Moh fly ash concrete. Moreover, not only low in LOI

amount, majority of its particles are in spherical shape, which helps to decrease water

demand of mixtures and therefore enhance workability of fresh concrete [15]. The

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low LOI of Thai fly ash is considered to be due to high allowable burning temperature

of the coal powder in Thailand [16].

1.2 Statement of problems

The proportion of low LOI fly ash is decreasing worldwide as an indirect result

of controlling toxic gases such as nitrogen oxides (NOx) to meet the emission

standards of the 1990 Clean Air Act amendments [17]. More recent coal power plants

around the world, including BLCP power plant, Thailand, are equipped with low-

NOx burners in their boilers, which are operated at lower firing temperature. This

example of approach has an adverse effect on the quality of the produced fly ash due

to the increasing amount of residual unburned carbon in the fly ash. Additionally,

activated carbon, injected to control mercury emission from coal-fired combustion

systems, can increase the carbon level in fly ash even more [18]. The maximum Loss

on Ignition (LOI) for different coal-using countries shown in Table 1.1 demonstrates

that apart from China and Russia, which allow for relatively high LOI values for

certain ashes, the other major coal-consuming countries stipulate similar lower LOI

limits for fly ash use in concrete production due to the fact that high LOI fly ash is

generally known to cause some malfunctions in concrete, which are probably known

to include discoloration, poor air entrainment ability, more water requirement and low

compressive strength [13],[14],[19].

High level of unburned carbon in fly ash hinders its further utilization in

cement and concrete industry. In 2006, 40 million tons of high LOI fly ash in the

United States was placed in landfills [18]. Disposal of fly ash is not only wasteful

manner of potential valuable resources but also money for transportation and disposal

charges. Moreover, it leads to environmental problems [20]. Some amount of high

LOI fly ash and other off-spec fly ash are utilized in low-value method such as using

as a landfill material, soil improvement, road base and raw material for producing

cement. The most effective use of fly ash at present, considering both volume and

value, is still in the area of concrete. So, in order to utilize these high LOI fly ashes in

the concrete work, the unburned carbon, which is an undesirable component, needs to

be reduced either by optimized combustion process or by efficient separation

techniques [21-25].

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Both the disposal and the carbon reduction processes of fly ash are difficult

and required large budget and time in the process. Therefore, better understanding of

high LOI fly ash concrete behavior is crucial to be capable of using it directly in

concrete work. However, it is also clear that the absolute quantity of unburned carbon

alone is not sufficient to judge the suitability of a fly ash for use in concrete

production. To determine precisely that suitability, the actual morphological

properties of high LOI fly ash need to be taken into account. Some studies found that

high carbon content did not have any detrimental influence on the concrete mixture.

Since fly ash having higher %LOI is finer than that having lower LOI. So it might be

the fineness that contributes high strength to the mix and cover the effect of carbon in

fly ash [26-27]. Moreover, a study by Coppola [28] indicated that fly ash with the

highest LOI content (11.30%) performed significantly better than the fly ash with the

lowest LOI content (4.19%) in term of concrete compressive strength development.

Table 1.1 Summary of maximum allowable %LOI of fly ash for use in

cement/concrete in different coal-using countries [20]

Countries LOI limits, %, maximum

Australia 3-6

Canada 3-10

China 5-15

EU

Type A: 5

Type B: 2-7

Type C: 4-9

India 5

Thailand 6

Japan 3-8

Russia Basic ash: 3-5

Acid ash: 2-25

South Africa 5

USA Class F: 6 (12)

Class C: 6

1.3 Objectives

According to the above discussion, the aims of this project are as follows:

To investigate the effects of LOI of fly ash on mechanical properties and

durability of concrete.

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To clarify and be able to explain the behavior of high LOI fly ash, when

its %LOI increase from low to high.

1.4 Scope of study

For the scope of this study, various parameters are studied within the following

scopes.

a) Materials

Type of cement: Ordinary Portland Cement Type I

Type of fly ash: - an original low LOI fly ash (high CaO) from Mae-Moh

power plant, having %LOI of 0.77%

- 4 artificial high LOI fly ashes synthesized by the

blending of low LOI fly ash and powdered activated

carbon (PAC), having different %LOI of

approximately 6%, 12%, 18% and 25%.

b) Paste mixtures

Water to binder ratio: 0.25 and 0.40

Amount of fly ash: 20%

c) Concrete mixtures

Water to binder ratio: 0.4 and 0.5

Amount of fly ash: 0%, 20% and 40% by weight of total binder

d) Experimental programs

Water requirement of mortar

Slump

Compressive strength

Autogenous shrinkage

Total shrinkage

Carbonation

Rapid chloride penetration test

Porosity of concrete

Micro hardness

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Chapter 2

Literature Review

2.1 Fly ash

Fly ash, the most commonly used pozzolan in concrete, is a by-product from

the combustion of pulverized coal in electricity power plants. In addition to

economics and ecological benefits, the use of fly ash in concrete is generally known

to improve many properties of fresh and hardened concrete.

Pozzolans are siliceous or siliceous and aluminous materials which them

selves process little or no hydration reaction. However, in a finely divided form, these

substances can chemically react with the calcium hydroxide in the presence of

moisture to form the compounds that have cementitious properties (ASTM standard

C618-80). This reaction is called the pozzolanic reaction. Fly ashes act as pozzolanic

materials when mixed with portland cement and water, by reacting with the calcium

hydroxide released by the hydration of Portland cement to produce various calcium-

silicate hydrates (C-S-H) and calcium-aluminate hydrates. Some fly ashes with higher

amounts of calcium will also display cementitious behavior by reacting with water to

produce hydrates in the absence of a source of calcium hydroxide. These pozzolanic

reactions are beneficial to the concrete in that they increase the quantity of the product

of cementitious binder phase (C-S-H) and, to a lesser extent, calcium-aluminate

hydrates, improving the long term strength and reducing the permeability of the

system. Both of these mechanisms enhance the durability of the concrete [29].

Since fly ash is a by-product, its properties depend on many factors such as:

the characteristics of its origin coal, combustion system design and operating

conditions, collecting process, etc. The performance of fly ash in concrete is greatly

influenced by its physical, mineralogical and chemical properties. Fly ashes can be

used in the concrete industry if its properties conform to the standard specifications

for fly ash used in concrete.

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2.1.1 Chemical composition and mineralogical of fly ash

The chemical composition and mineralogical properties of fly ash depend

mainly upon the composition of original coal and combustion method. Generally, the

chemical composition of fly ash shows a wide diversity, but the major chemicals of

fly ash are SiO2 (25-60%), Al2O3 (10-30%), Fe2O3 (5-25%), CaO (1-35%). Figure 2.1

shows the position of fly ash with low calcium content in the ternary diagram SiO2-

Al2O3-CaO. Fly ashes can be classified into two groups as class C and class F

according to ASTM C-618. Class C fly ash, originated from lignitic coal, vastly has

CaO content higher than 10% and the sum of SiO2, Al2O3, Fe2O3 is higher than 50%.

Class F fly ash is originated from anthracite or bituminous coal. It consists of less

than 10% CaO and the sum of the major oxides is higher than 70%. The fly ash

generated recently tends to have lower value of SiO2 and higher carbon content [30].

Figure 2.1 Survey of products containing SiO2, Al2O3 and CaO [31]

Fly ash is a complex material consisting of heterogeneous combinations of

amorphous (glassy) and crystalline phases. The largest fraction of fly ash consists of

glassy spheres of two types, solid and hollow (cenospheres). These glassy phases are

typically 60 to 90% of the total mass of fly ash. The remaining fractions of fly ash are

made up of a variety of crystalline phases. These two phases are not completely

separated and independent of one another [32]. Unburned carbon particles are

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collected with the fly ash as particles of carbon, which may constitute up to 16% of

the total. The amount of unburned carbon in fly ash depends on the rate and

temperature of combustion, the degree of pulverization of the original coal, the

fuel/air ratio, the nature of the coal being burned, etc [33].

The carbon content in fly ash is a result of incomplete combustion of the coal

and organic additives used in the collection process. Carbon content is not usually

determined directly, a generally accepted test method for estimating the unburned

carbon content of fly ash is the determination of its loss on ignition or LOI [34].

However, in the LOI test method, it has been observed that LOI result may

overestimate the amount of the unburned carbon [35-36] as the ignition mass loss is

not only due to burning of organic carbon but also due to other possible reactions such

as calcination of inorganic carbonates, desorption of physically and chemically bound

water (e.g., dehydration of portlandite), and oxidation of sulfur and iron mineral. In

contrary, the presence of sulphides, sulphur, and some iron minerals will decrease the

LOI value due to gain in weight because of oxidation. However, the carbon seems to

be the substance most responsible for ignition loss [37]. Fly ash used in concrete

typically has %LOI less than 6%; however, ASTM C 618 mentions that the use of

class F fly ash with %LOI up to 12% can be used, if either acceptable performance

records or laboratory test results are made available.

2.1.2 Physical properties and morphology of fly ash

The morphology of fly ash particles is controlled by both the combustion

temperature and cooling rate. Fly ash can exist as round particles, angular particles,

cenospheres, plerospheres, broken pieces of coarser particles, or fused particles.

Generally fly ash comprises of spherical solids and hollow cenospheres [38]. The

majority of fly ash particles ranged in size from approximately 1 to 100 μm and

consisted of small solid spheres (Figure 2.2A), hollow cenospheres (Figure 2.2B),

irregularly shaped unburned carbon particles (Figure 2.2C), minerals and mineral

aggregates, such as the quartz (Figure 2.2D), agglomerated particles (Figure 2.2E) and

irregularly shape amorphous particles (Figure 2.2F). These physical properties of fly

ash such as particle shape, fineness, particle-size distribution, and density of fly ash

particles influence the properties and performances of fresh and hardened concrete.

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Lane and Best [40] reported that the shape of fly ash particles is also a function

of particle size. The majority of fly ash particles are glassy, solid, or hollow, and

spherical in shape. Examples of fly ash particle shapes are shown in Figures 2.2 and

2.3. Fly ash particles that are hollow are translucent to opaque, slightly to highly

porous, and vary in shape from rounded to elongated.

Figure 2.2 Backscattered electron (BSE) images of different fly ash particles

(A) typical fly ash spheres; (B) hollow cenosphere in cross-section; (C) unburned

carbon particle; (D) mineral aggregate (quartz); (E) agglomerated particles in cross-

section; (F) irregularly shaped amorphous particles [39].

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Styszko-Grochowiak et al [41] studied about characterization of the coal fly ash

for the purpose of improvement of industrial on-line measurement of unburned carbon

content. The conclusion of the study was found that the content of unburned carbon is

closely linked to the particle size distribution of fly ash. The content of unburned

carbon diminishes with the smaller size of particles of the fly ash.

2.1.3 High LOI fly ash

High LOI fly ash means fly ash that contains high amount of unburned carbon

content, since carbon is generally the substance most responsible for ignition loss

[37]. The terms loss on ignition (LOI) and content of carbon are often used

interchangeably. A generally acceptable test method to initially estimate the unburned

carbon content of fly ash is the determination test of its loss on ignition, or LOI test

(ASTM D7348). However, this test is not sufficient to identify the suitability of a fly

ash for the concrete industry, since this test only give an approximation to the carbon

content of a sample and provides no information about the form or properties of

carbon [13].

The factors affecting unburned carbon content or %LOI of fly ash were found to

come from these 2 major groups, which are the effect of coal characteristics and the

effect of combustion system design and operating conditions [42]. Moreover, the

widespread installation of low-NOx combustion systems is one of the most significant

problems in terms of increasing %LOI of fly ash. Higher level of %LOI of fly ash

hinders its further utilization in concrete industry, due to its drawbacks in fresh and

hardened concrete properties.

The unburned carbon particle (Figure 2.3a) has a porous structure. Some

spherical particles are attached to the external surface, and some are penetrated inside

the cavities and large pores of the unburned carbon particles (Figure 2.3b). The

variety in particle shape and pore structure of unburned carbon particles of fly ash

might be achieved depending on the 2 main factors mentioned above. The porous

characteristic of unburned carbon particles provides them a very good absorptive

ability. Freeman [13] found that hydrophobic end of air entraining agent (AEA),

which is used to stabilize air bubbles in concrete, is attached on carbon surface area

consisting of the external surface of carbonaceous particle and some internal surfaces

of larger pores. This results in rendering them unavailable for attachment to air

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bubbles and this low-entrained-air concrete will have less resistance to freezing and

thawing cycles. Other effects of those unburned carbon content of fly ash on

properties of concrete are known to include discoloration, poor air entrainment ability,

high water requirement, low compressive strength and mixture segregation.

(a) x250 (b) x3000

Figure 2.3 SEM images of unburned carbon particles [43]

2.2 Standard specifications of fly ash for use in concrete

2.2.1 ASTM standard

There are various schemes of fly ash classification. In the United States, the

specification which is used for evaluating suitability of fly ash is ASTM C618 [8],

“Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for

Use in Concrete”. This specification classifies fly ash into two major classes i.e. class

C and class F based on the chemical composition and the initial coal (Table 2.1).

Generally, class F is the result of combusting anthracite or bituminous coal while

class C fly ash is formed by combustion of lignite or sub-bituminous coal. LOI

represents the amount of unburned carbon in fly ash. As existing carbon is not ideal

for concrete especially in terms of air entraining, LOI is limited to 6% by ASTM.

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Table 2.1 Chemical properties requirements for fly ash used as mineral admixtures

in Portland cement concrete according to ASTM C618

Characteristic Requirements

Class F Class C

SiO2+Al2O3+Fe2O3, min % 70 50

SO3, max % 5.0 5.0

Moisture content, max % 3.0 3.0

LOI, max % 6.0 6.0

2.2.2 Vietnamese standard

According to TCVN 10302, which is the specification of fly ash for concrete

and mortar in Vietnam, fly ashes are also classified into 2 major classes, which are

class F and class C fly ashes (Table 2.2). The classification of Vietnamese fly ash

specification is based on the chemical compositions of fly ash such as: the total

summation of the 3 major chemical constituents of fly ash, sulfur, free calcium oxide

and LOI percentage of fly ash. Moreover, specification of fly ash in Vietnam also

classified fly ash into 5 groups, by considering the applications level of the fly ash.

- Application a: for reinforced concrete products and components made

from normal concrete and lightweight concrete

- Application b: for non-reinforced concrete products and components made

from normal concrete, lightweight concrete and mortar

- Application c: for concrete products and components made from cellular

concrete

- Application d: for reinforced concrete products and components exposed

to special conditions.

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Table 2.2 Specifications of fly ash for concrete and mortar according to TCVN

10302:2013 [11]

Characteristics Fly ash

type

Application level

a b c d

1. Total oxides (SiO2+Al2O3+Fe2O3), %

mass, Min.

F

C

70

45

2. Sulfur trioxide SO3, % mass, Max. F

C

3

5

3

5

3

6

3

3

3. Free calcium oxide CaO, % mass, Max. F

C

-

2

-

4

-

4

-

2

4. Loss on Ignition (LOI), % mass, Max. F

C

12

5

15

9

8*

7

5*

5

5. Harmful alkali (soluble alkali), % mass,

Max

F

C 1.5

6. Moisture content, % mass, Max. F

C 3

7. Retaining on 45m sieve, % mass, Max. F

C 25 34 40 18

8. Water demand over control, % mass, Max. F

C 105 105 100 105

9. Content of ion Cl-,% mass, Max F

C 0.1 - - 0.1

10. Natural radioactivity Aeff, (Bq/kg) of fly

ash for:

- Civil, public building, Max.

- Industrial building, urban and municipal

road, Max

370

740

* When burning anthracite coal, fly ash with LOI up to 12% and 10% maybe approved

for the applications c and d, respectively according to the agreement with users or

accepted laboratory testing results.

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2.2.3 Thai standard

According to TIS 2135 [9], “Coal fly ash for use as an admixture in concrete”,

Thai Industrial Standards Institute, fly ashes used in concrete are classified into 3

classes: class 1, class 2 and class 3 (Table 2.3). Most of the fly ashes are in class 2

which are separated into types 2a and 2b. Class 2a requires percentage of calcium

oxide (CaO) less than 10 %, whereas class 2b contains CaO not less than 10 %.

Table 2.3 Chemical properties, specification of fly ash according to TIS 2135 [9]

Item Properties

Requirement

Class 1 Class 2 Class 3

Type a Type b

1 Silicon dioxide (SiO2), min % 30.0 30.0 30.0 30.0

2 Calcium oxide (CaO), % - Less than

10.0

Not less

than 10.0

-

3 Sulfur trioxide (SO3), max% 5.0 5.0 5.0 5.0

4 Moisture content, max % 3.0 3.0 2.0 12.0

5 LOI content, max % 6.01) 6.01) 6.01) 6.01)

2.2.4 Japanese standard

The Japan Industrial Standard (JIS) A 6201 [10], “Fly Ash for Use in

Concrete,” classifies fly ash as Types I, II, III, and IV (see Table 2.4) mainly on their

%LOI and fineness described as follows:

• High-quality fly ash with LOI less than 3.0% and Blaine fineness higher than

5000 cm2/g is specified as Type I.

• Most of the fly ash qualified in JIS A 6201-1996 is specified as Type II.

• Fly ash with high LOI ranging from 5.0 to 8.0% is specified as Type III.

• Fly ash with low Blaine fineness ranging from 1500 to 2500 cm2/g is specified

as Type IV.

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Table 2.4 Standard specifications of fly ash according to JIS-A 6201-1999

Item Type I Type II Type

III Type IV

Silica dioxide (%) 45.0 or higher

Moisture content (%) 1.0 or less

Ignition Loss (%) 3.0 or

less

5.0 or

less

8.0 or

less

5.0 or

less

Density (g/cm3) 1.95 or higher

Fineness

Residue on 45m sieve

(screen sieve method) (%)

10 or

less

40 or

less

40 or

less

70 or

less

Specific surface area (Blaine

method) (cm2/g)

5000 or

higher

2500 or

higher

2500 or

higher

1500 or

higher

Flow value ratio (%) 105 or

higher

80 or

higher

80 or

higher

60 or

higher

Activity

index

(%)

Material age: 28 days 90 or

higher

80 or

higher

80 or

higher

60 or

higher

Material age: 91 days 100 or

higher

90 or

higher

90 or

higher

70 or

higher

2.3 Effect of fly ash on concrete properties

2.3.1 Effect of fly ash on properties of fresh concrete

Owens [44] reported that the use of fly ash containing a larger fraction of

particles coarser than 45μm or a fly ash with high amount of unburned carbon and

loss on ignition more than 1% resulted in higher water demand.

Lewandowski [45] reported that the reduction of the water demand of concrete

with a constant spread of 42 cm was distinctly greater for fly ash with an ignition loss

of 3.6 % by mass than for an ignition loss of 9.3% by mass (Figure 2.4)

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Figure 2.4 Reduction of water demand of fresh concrete with a spread of 42 cm due

to substitution of fly ash for Portland cement Z 35 fly ashes with loss on ignition of

3.6% (F3) and 9.3% (F9) [45]

Siddique [46] investigated the effect of fly ash on slump of fresh concrete.

Most of the tested fly ashes were class F type with %LOI of 1.9%, replacing Portland

cement with three percentages (40%, 45%, and 50%). When fly ash content of

mixtures increased, their slump increased. On the other hand, slump of fresh concrete

with fly ash was higher than that of cement only.

Amonamarittakul [15] conducted a research using one fly ash from Mae-Moh

power plant and 4 fly ashes from BLCP power plants. Mae-Moh fly ash is high CaO

fly ash with very low %LOI of 0.14% while BLCP fly ashes are low CaO fly ashes

having %LOI from 2.57%, 3.29%, 3.78% and 4.09%. It was found that low LOI

content and spherical particles shape of fly ash can reduce water requirements of fly

ash concrete. Fly ash that has the lowest LOI content and most spherical particle

shape requires less water than other fly ashes to obtain the same water requirement of

mortar and slump of concrete.

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2.3.2 Effect of fly ash on compressive strength of concrete

Hornain [26] investigated the effect of residual carbon content in fly ash on the

hardened cement paste properties. Fly ashes with three percentages residual carbon

were used: 4, 7, and 12%. The order of fineness is the fly ash with 12, 7, and 5%.

Their results show that strength of fly ash with 12% is not different from that with 7

and 5% and is lower than that of the normal cement specimens. The strength of these

fly ash mortars increase with time. They conclude that the high carbon content did not

have any detrimental influence on strength of the concrete mixture. Since fly ash with

12% is finer than 5% so it might be this fineness that contributes high strength to the

mix and covers the effect of carbon in the fly ash. In order to investigate the effect of

carbon on strength, the fly ashes used for testing should have the same fineness.

Bumrongjaroen, W [30] studied about utilization of processed fly ash in mortar.

Several types of fly ashes, which are wet bottom, dry bottom and low NOx fly ashes

were used. The fly ash from the original feed of dry bottom ash and wet bottom ash

have LOI about 2.05 to 4.57% of carbon, while the fly ash from low NOx ash has LOI

of about 12.5% of carbon. All fly ashes were ground to different particle size

distributions. It was found that the grinding method is an effective means to process

raw wet bottom, dry bottom, and low NOx fly ash in to beneficial products. The

quality of fly ash increases significantly after grinding. With cement replacement up

to 42%, the strength of ground fly ash mortar performed as well as or better than plain

cement mortar after 14 days. It was proved that ground fly ash increases the strength

properties of mortar because its fineness enhances the three mechanisms operating for

strength gain: dispersion, nucleation, and pozzolanic activity. The dispersion function

of fly ash was observed from the pore size distribution of the 5-minute paste. When

fly ash was present, the cement grains were more dispersed, resulting in a finer pore

size distribution. The pore size reduction at age of 28 days could be a result of both

nucleation and pozzolanic action. The evidence of nucleation is the thicker hydration

products on fly ash particles and the evidence of pozzolanic action are the

deterioration in some fly ash particles as well as the depletion of calcium hydroxide

content. It was also found that the ground fly ash mortar with high carbon content

performs better than that of normal mortar and the ground fly ash mortar without

carbon.

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Fox and Constantiner [47] studied the influence of fly ash after change to Low-

NOx Burners (LNB) on concrete strength. Samples of fly ash before and after the

change to LNB were collected at a plant consistently burning southern lignite from

one mine. The strength activity index according to ASTM C311, affinity for air-

entraining admixtures, chemical composition, particle size and shape, glass content,

and phase assemblage by quantitative x-ray diffraction were tested. Strength activity

index at 3, 7, 28 and 56 days for low-NOx fly ash were consistently 10% lower than

the corresponding values for the fly ash before the burner change. There is no

significant change in chemical composition between samples taken before and after

the LNB installation. Fly ash produced after LNB went online has slightly higher

active carbon contents, more coarse particles, and slightly less glass, which can

explain the reduction of its strength activity index.

Amonamarittakul [15] conducted a research using one fly ash from Mae-Moh

power plant and 4 fly ashes from BLCP power plants. Mae-Moh fly ash is high CaO

fly ash having CaO content of 20.91% and very low %LOI of 0.14% while BLCP fly

ashes are low CaO fly ashes having CaO in range between 0.75% to 2.13% and %LOI

from 2.57%, 3.29%, 3.78% and 4.09%. The results found that regarding chemical

composition, CaO content is an important parameter that has influence on the early

age strength development. The early age compressive strength of high CaO fly ash

(Mae-Moh fly ash) is higher than that of the low CaO fly ash. However, compressive

strength of low CaO fly ashes from BLCP power plant are slightly higher than that of

the Mae-Moh fly ash at later ages due to the higher dissolution content of pozzolanic

materials (SiO2, Al2O3).

Siddique [48] studied the strength of concrete containing class F fly ash with

%LOI of 1.9%, using 3 replacement percentages, which are 40%, 45%, and 50%. It

was found that all replacement percentages of fly ash reduced the compressive

strength of concrete at 28 days, but there was a continuous and significant

improvement of strength properties beyond 28 days. However, the strength of

concrete with 40%, 45% and 50% fly ash content at 28 days is sufficient for use in

reinforced cement concrete construction.

Cengiz Duran Atis [19] studied the effect of LOI in high volume fly ash

concrete made with and without superplasticizer. The experiment was conducted

using two fly ashes from the electricity generating Drax and Aberthaw power stations

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in England. The %LOI of Drax and Abethaw fly ashes are of 2.80% and 15.60%,

respectively. Fly ashes were used to replace cement with replacement levels of 50 and

70 mass %. The results of this study showed that Drax fly ash had the ability to

reduce the water demand of a concrete mixture. Aberthaw fly ash, which is a high

LOI fly ash, increased the water demand of concrete due to its high LOI content. In

term of compressive strength, Drax fly ash developed higher strength than the

Aberthaw fly ash. The concrete containing 50% Drax fly ash developed high strength,

while 70% fly ash replacement concrete developed moderate strength. Using fly ash

replacement of 50%, Aberthaw fly ash developed satisfactory strength at 28 days and

high strength at 1 year.

Coppola et al [28] studied compressive strength of concrete using four fly ashes

(A, B, C, D). Fly ash A and D came from two different coal fired generating plants,

whereas fly ash B and C were produced by mixing the other two materials. The main

difference between these products is the LOI level, which change from a minimum

level of 4.19% for the fly ash A up to a maximum of 11.3% for fly ash D. The

increase in the LOI level was accompanied by a decrease in the specific gravity which

changed from 0.68 kg/l for the fly ash D to 0.88 kg/l for the fly ash A. Two reference

mixtures, without fly ash, were produced with the same amount of mixing water

(200kg/m3) and different cement factors, 417 kg/m3 and 294 kg/m3, for the reference

concrete R1 and R2, respectively. Therefore, the adopted w/c was 0.48 and 0.68 for

the reference mixtures R1 and R2, respectively. A naphthalene base superplasticizer

was used in concrete containing fly ash B, C and D in order to obtain approximately

the same slump level (180-200mm) as the reference mixtures. It was surprising to

record that there was no relationship between the fly ash LOI content and the concrete

compressive strength development. As a matter of fact, the fly ash D with the highest

LOI content (11.30%) performed significantly better than the fly ash A with the

lowest LOI content. This could be ascribed to the specific composition of fly ash D,

which acted as a better pozzolan in spite of higher amount of the LOI material.

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2.3.3 Effect of fly ash on durability of concrete

Sudsangium [49] investigated the applicability of Mae-Moh fly ashes which

contain different SO3 contents as a solution to reduce autogenous shrinkage and

compared them with a fly ash from Hong Kong. The effect of autogenous shrinkage

in terms of compressive strength, flexural strength and setting of cement pastes with

and without Mae-Moh fly ashes and fly ash from Hong Kong were examined. From

the test results, it was concluded that under sealed condition, fly ashes could be used

for reducing autogenous shrinkage by their spherical particles which led to larger free

water content and SO3 content of Mae- Moh fly ashes. The higher SO

3 content is, the

larger autogenous shrinkage reduction was obtained. Mae- Moh fly ashes were more

effective in improving compressive strength and flexural strength than the fly ash

from Hong Kong.

Tangtermsirikul [50] studied the effect of fly ashes with various chemical

compositions, particle sizes and replacement percentages on autogenous shrinkage of

the pastes with fly ashes. It was found that for the effect of chemical composition, fly

ash with higher SO3 content resulted in lower autogenous shrinkage. For the effect of

particle size, paste with fly ash having smaller average size than cement exhibited

larger autogenous shrinkage whereas pastes with fly ash having bigger size than

cement showed smaller autogenous shrinkage than that of the reference cement paste.

For the effect of fly ash content, non- classified and classified fly ash having larger

average size than cement showed the same tendency i.e. larger autogenous shrinkage

in 20% fly ash paste than in 50% fly ash paste when non-classified fly ash was used.

On the other hand, smaller autogenous shrinkage in 20% fly ash paste than in 50% fly

ash paste was found in case of pastes with classified fly ash having smaller average

size than cement. It could be concluded that not only chemical composition which

affects rate of hardening and volume change of pastes with fly ash but also particle

size, which affects the pore structure of the paste, has to be considered for modeling

autogenous shrinkage of pastes with fly ash.

Tongaroonsri [51] indicated that spherical shape of fly ash particles seemed to

be the main factor that caused less water retainability than the irregular cement

particles did. This resulted in larger free water content in the mixtures with fly ash

than in the mixtures without fly ash when prepared with the same w/b. As autogenous

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shrinkage is the result of water consumption in the hydration process, larger free

water content can reduce the shrinkage. Moreover, pozzolanic reaction of fly ash

proceeds slowly. Also when a part of cement is replaced by fly ash, the cement

hydration reaction is retarded.

Subsomboon [52] studied the effect of Mae-Moh fly ash on shrinkage and

swelling of cement paste. The specimens were controlled, by using replacement

percentages of fly ash at 0, 30 and 50%. The results revealed that the drying shrinkage

decreased by increasing replacement percentage of fly ash.

Pacheerat [53] studied the effect of water to binder ratio and replacement

percentage of fly ash on the length change including the comparison of length change

between mortar and concrete. Fly ash was used at 0, 15, 30, 45 and 60% replacement

by weight of cement run on a series of water to binder ratios at 0.35, 0.50 and 0.65.

From the test results, it was found that the length change of concrete showed the same

trend as mortar but the values were lower for all mixes. When increasing water to

binder ratio, the expansion and drying shrinkage increased while autogenous

shrinkage decreased. When increasing replacement percentage of fly ash, all length

changes decreased.

Chindaprasirt et al. [54] studied the influence of fly ash on water demand and

some properties of hardened mortars. In addition to the original fly ash (OFA), five

different fineness values of fly ash were obtained by sieving and by using an air

separator. The fly ash dosage of 40% by weight of binder was used for the entire

experiment. It was found that the compressive strength of mortar containing fine fly

ash was better than that of original fly ash mortar at all ages. The mixture containing

very fine fly ash gives the highest strength. Although, the use of all fly ashes with all

fineness was significantly reduced the drying shrinkage, the mixture containing coarse

fly ash showed the least improvement. The results of the study suggested that using

fine fly ash resulted in a denser cement matrix and better mechanical properties of

mortar, since it is more reactive.

Ho and Lewis [55] found that the influence of using fly ash as a replacement

material in concrete increased the rate of carbonation due to increasing of porosity in

concrete.

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Khunthongkeaw et al [56] studied carbonation of concrete by using two types of

fly ash with different CaO contents. The decreased ratio of water to binder and fly ash

content led to a better carbonation resistance. For the same fly ash content, specimens

with high-CaO fly ash showed a better carbonation resistance than those of low-CaO

fly ash. This is partly because the tested mixtures with high-CaO fly ash (FA2)

exhibited a lower porosity. Also pH was higher than those with low-CaO fly ash

(FA1) [57]. The results also revealed that when the samples incorporated 10% of fly

ash in the binder, the carbonation coefficients only slightly increased from the

cement-only sample. This increment was drastic when the fly ash content was higher

than 30%. At the fly ash content of 50%, the carbonation coefficient was

approximately two to three times as large as that of the cement-only mixture.

T.-H Ha et al [14] studied the effect of unburned carbon on the corrosion performance

of fly ash mortars. The study used carbon admixed fly ash in order to vary the

percentage LOI of fly ash from 2 to 24%. The results found that the increase in

activated carbon content accelerated the corrosion of rebars in ordinary Portland

cement (OPC) mortars containing fly ash with different percentages of carbon. The

alkalinity of the cement was greatly affected with increased carbon content, and when

the quantity of carbon was increased, cement lost its characteristic color. More than

60% area of rebar steel was rusted. The study suggested that the upper limit of

replacement for various admixed carbon system, under aggressive alternate wetting

and drying condition with 3% NaCl, was 6-8%.

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Chapter 3

Experimental Program

3.1 General

In order to investigate the effect of high LOI fly ash on properties of concrete,

artificial high LOI fly ashes with LOI levels of 0, 6, 12, 18 and 25%, prepared by

blending low LOI fly ash with powdered activated carbon (PAC), were used as a

cement replacing material throughout the entire experiment. The ratio of paste volume

to void volume of aggregate phase of 1.4 was used for all mixtures. In this study, fine

aggregate was natural river sand and coarse aggregate was crushed limestone with a

maximum size of 20 mm. The properties of aggregate complied with the requirement

of ASTM C33 [58]. The specific gravities of fine and coarse aggregates based on

saturated surface dry condition (SSD) were 2.59 and 2.83, respectively (Appendix A).

The ratio by volume of sand to total aggregate of 0.43 giving a minimum void ratio of

0.23 was selected for mix proportions of concrete.

3.2 Materials

3.2.1 Cement

Ordinary Portland cement type I was used. Chemical composition and physical

properties of the cement are shown in Tables 3.1 and Table 3.2, respectively.

3.2.2 Fly ashes

Low LOI fly ash from Mae-Moh power plant was used as a cement replacing

material. Mae-Moh fly ash could be classified as class F fly ash according to ASTM

C618 and class 2b according to TIS 2135. Chemical composition and physical

properties of a Mae-Moh fly ash sample are shown in Tables 3.1 and 3.2,

respectively. Figure 3.1a shows a picture of Mae-Moh fly ash.

In order to make artificial high LOI fly ashes, it is important to know how the

unburned carbon particles in the real high LOI fly ash actually are. Thus, the

characteristic of 2 high LOI fly ashes, one from BLCP power plant, Thailand (see

Figure 3.1b) and another one from a Vietnamese power plant (Figure 3.1c) were

investigated. The high LOI fly ash from Vietnam was used in this experiment as the

archetype for making artificial high LOI fly ashes.

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(a) Mae-Moh (b) BLCP (c) Vietnam

Figure 3.1 Fly ash from different sources

Table 3.1 Chemical compositions of cement and fly ash

Chemical composition Cement Mae-Moh fly ash

SiO2 18.93 35.71

Al2O3 5.51 20.44

Fe2O3 3.31 15.54

CaO 65.53 16.52

MgO 1.24 2.00

Na2O 0.15 1.15

K2O 0.31 2.41

SO3 2.88 4.26

LOI 1.89 0.77

Freelime - 1.71

Table 3.2 Physical properties of cement and fly ash

Physical properties Cement Mae-Moh Fly ash

Specific gravity 3.15 2.21

Blaine fineness (cm2/g) 3100 2867

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3.2.3 Activated carbon (AC)

Powdered Activated Carbons (PACs) used in this experiment were selected

from 3 different available sources of activated carbon in Thailand (Figures 3.2a to

3.2c) i.e coconut shell (CS), bituminous coal (BC) and wood (W). The shape of

activated carbon produced from coconut shell and bituminous coal are granular while

the activated carbon produced from wood is powdery. Therefore, the granular

activated carbon were ground to powder. The LOI of PACs from coconut shell,

bituminous coal and wood were 85.28%, 86.18%, and 80.37%, respectively.

Chemical compositions of all PACs tested by X-ray fluorescence (XRF) are shown in

Table 3.3. PAC selection was considered based on their physical properties,

especially the particle shape characteristic by Scanning Electron Microscopy (SEM).

Table 3.3 Chemical compositions of powdered activated carbons (PACs)

Chemical composition PAC-CS PAC-C PAC-W

SiO2 0.39 3.82 1.10

Al2O3 0.14 1.54 0.31

Fe2O3 0.10 0.36 2.89

CaO 0.16 0.25 0.36

MgO 0.21 - 0.59

Na2O 0.55 - 0.19

K2O 1.61 - 1.05

SO3 - 0.90 0.31

LOI 85.28 86.18 80.37

(a) AC-CS (b) AC-BC (c) AC-W

Figure 3.2 Particle shapes of activated carbon (AC) from different sources

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3.3 PAC selection and preparation

In PAC selection process, carbon content of each fly ash and PAC was

determined by the loss on ignition (LOI) test. Particle shape and pore structure of all

fly ashes and PACs, were investigated by Scanning Electron Microscopy (SEM).

Only the PAC that is the most similar, mainly in term of particle shape and pore

structure, to the unburned carbon particles of Vietnamese fly ash (UC-FV) was

selected.

After the suitable PAC was selected for making artificial high LOI fly ashes, it

was ground to have similar particle size distribution to the unburned carbon particles

of Vietnamese fly ash by using the planetary ball mill (see Figure 3.3). The grinding

procedure of powdered activated carbon was accordingly processed as shown by the

flowchart in Figure 3.4. The grinding parameters consist of rotational speed (rpm),

grinding time, grinding repetitions and quantity of mill balls. In this study, 100g of

PAC were ground each time with 25 mill balls at a rotational speed of 500 rpm for 5

minutes. The grinding repetition was done for 3 times. Particle size distribution of

unburned carbon particles of Vietnamese fly ash was determined by using wet sieve

analysis method and the amount of carbon retained in each size range is also

measured by LOI test. Vietnamese fly ash was sieved into different sizes: #30, 50,

100, 200 and 325. Particle size distribution of the fly ash measuring by wet sieving

method was conducted by calculating the weight percentage of fly ash retained on the

sieve. Size distribution of unburned carbon of Vietnamese fly ash of each sieve was

measured by calculating the weight percentage of carbon burnt out at 950°C. The

grinding process was repeated by adjusting the grinding conditions such as grinding

time, grinding repetitions and number of metal balls until the similar size distributions

of UC-FV and PAC were achieved. After that, the mix proportions of Mae-Moh fly

ash and PAC for making artificial high LOI fly ashes were calculated as shown in

Appendix B. Finally, the artificial high LOI fly ashes were then made, by mixing the

selected PAC with the low LOI fly ash from Mae-Moh power plant. The designated

%LOI of fly ashes were 0%, 6%, 12%, 18% and 25%.

Ref. code: 25605722040416SAT

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Figure 3.3 Planetary ball mill

Figure 3.4 Grinding process of powdered activated carbon (PAC)

Check size distribution of

UC-FV

(Reference)

Grind the Activated Carbon (AC)

Into PAC

Check Size Distribution of PAC

With UC-FV

Similar Finish

Much

Different

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Basic properties of

Artificial high LOI fly ash

- Loss on ignition

- Specific gravity

- Moisture content

- Blaine fineness

- Water retainability

-Water requirement

Clarification

Slump


Slump model

Porosity

SEM

Micro hardness

Experimental Program

Basic and mechanical properties of

high LOI fly ash concrete

Durability of

High LOI fly ash concrete

Carbonation

Rapid Chloride Penetration Test

Shrinkage

Figure 3.5 Schematic outline of this study

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3.4 Experimental Methodology

This section describes details of test procedures, mix proportions and specimen

preparation for each experiment conducted in this study. The research scheme is

shown in Figure 3.5. The experiments include basic properties of artificial high LOI

fly ashes, basic and mechanical properties of the high LOI fly ash concrete. Some

durability properties of high LOI fly ash paste and concrete were also investigated.

Moreover, microstructure of high LOI fly ash concrete was also studied.

3.4.1 Properties of artificial high LOI fly ash

After all the artificial high LOI fly ashes had been made, the basic properties

such as LOI test, moisture content, specific gravity, Blaine fineness, particle size

distribution, water retainability and water requirement were tested.

3.4.1.1 Loss on Ignition

LOI test was carried out according to ASTM D7348 [34]. The apparatus for

LOI test are shown in Figures 3.6a to 3.6d. Place the samples for LOI test without

cover into preheated drying oven (104 to 110°C). Close the oven and heat for 1h to

eliminate the moisture. After that, remove the samples and cover immediately, allow

to cool off to ambient temperature in a desiccator. After the samples has cool down.

Place approximately 1 g of combustion residue into a pre-weighed crucible and weigh

the test specimen to the nearest 0.1 mg. Place the crucibles with the test specimen,

without a cover, into the cold furnace. Raise the temperature of the furnace at a rate

such that the furnace temperature reaches 450 to 500°C at the end of first hour and

950°C at the end of the second hour. Maintain the temperature for an additional two

hours or until the combustion residue test specimens reach a constant mass.

Calculate the percentage of loss on ignition to the nearest 0.1, as follows:

LOI, % =

A

B × 100 (3.1)

where :

A = loss in mass between 105°C and 950 °C

B = mass of moisture-free sample used

Ref. code: 25605722040416SAT

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a) Crucibles b) Balance

c) Oven d) Muffle furnace

Figure 3.6 Apparatus for LOI test

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3.4.1.2 Water retainability

Water retainability of a powder material is the water restricted by the powder

material, which includes water absorbed in the powder and that retained on its

surface. Tangtermsirikul and Kitticharoeniat [59] introduced an easy method for

estimating the water retainability of powder materials by finding a point of lowest

water to powder material ratio by weight that initiates slump of paste using a mini-

slump test (see Figure 3.7).

A metal mold, in the form of a frustum of a cone with dimensions as follows:

403 mm inside diameter at the top, 903 mm inside diameter at the bottom and 753

mm in height, and a metal tamper, weighing 34015 g and having a flat circular

tamping face 253 mm in diameter, are used in the mini slump test.

The test was first started by mixing the powder paste with a guessed value of

water to powder material ratio starting from a low ratio so that the mixture has no

slump. The mixture, approximately one third of the volume of the mold, is placed in

the mold and tamped 25 times with the tamper. The other two portions of the mixture

are placed and tamped until the mold is full. The excess is struck off and the mold is

immediately removed by raising it carefully in the vertical direction. The slump of the

mixture is measured. The entire process is repeated by increasing the water to powder

material ratio until slump is initiated. The water to powder material ratio, which

initiates slump, is the water retainability coefficient (β) of that powder material.

Figure 3.7 Mini slump test

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3.4.2 Basic and mechanical properties of high LOI fly ash concrete

The designation of mix proportion is labeled with the following nomenclature

(see Figure 3.8). W represents water to binder ratio of a mixture. W40 is water to

binder ratio of 0.4. OPC is cement only mixture (Ordinary Portland Cement type I).

FM is the mixture containing Mae-Moh fly ash. The number behind the letter FM

represents an approximate %LOI of the fly ash, which in this experiment ranges

approximately from 0.77% to 6, 12, 18 and 25%. r20 is the replacement percentage of

fly ash of 20%.

W40 OPC FM 12 r20

Figure 3.8 Mixture designation nomenclature

3.4.2.1 Slump

In order to investigate the effect of high LOI fly ash on workability of fresh

concrete, slump test was conducted according to the ASTM C143 [60]. The apparatus

for slump test is shown in Figure 3.9. After finishing concrete mixing, slump of the

fresh concrete was instantly measured and recorded as initial slump. In this study,

slump of concrete with high LOI fly ash, having %LOI of 0, 6, 12, 18 and 25%, were

tested in two w/b, which are 0.4 and 0.5. The details of all mix proportions for slump

test are shown in Table 3.4.

Water to binder

ratio LOI percentage of

fly ash

Containing fly ash Replacement

percentage

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Table 3.4 Mix proportions of concrete for slump test

Figure 3.9 Apparatus for slump test

kg kg kg kg kg

1 W40OPC 1.4 - 450.48 0.00 742.62 1075.62 180.19

2 W40FM0r20 1.4 20 347.31 86.83 742.62 1075.62 173.65

3 W40FM6r20 1.4 20 347.31 86.83 742.62 1075.62 173.65

4 W40FM12r20 1.4 20 347.31 86.83 742.62 1075.62 173.65

5 W40FM18r20 1.4 20 347.31 86.83 742.62 1075.62 173.65

6 W40FM25r20 1.4 20 347.31 86.83 742.62 1075.62 173.65

7 W40FM0r40 1.4 40 251.36 167.58 742.62 1075.62 167.58

8 W40FM6r40 1.4 40 251.36 167.58 742.62 1075.62 167.58

9 W40FM12r40 1.4 40 251.36 167.58 742.62 1075.62 167.58

10 W40FM18r40 1.4 40 251.36 167.58 742.62 1075.62 167.58

11 W40FM25r40 1.4 40 251.36 167.58 742.62 1075.62 167.58

12 W50OPC 1.4 - 395.37 0.00 742.62 1075.62 197.69

13 W50FM0r20 1.4 20 306.18 76.55 742.62 1075.62 191.36

14 W50FM6r20 1.4 20 306.18 76.55 742.62 1075.62 191.36

15 W50FM12r20 1.4 20 306.18 76.55 742.62 1075.62 191.36

16 W50FM18r20 1.4 20 306.18 76.55 742.62 1075.62 191.36

17 W50FM25r20 1.4 20 306.18 76.55 742.62 1075.62 191.36

18 W50FM0r40 1.4 40 222.52 148.35 742.62 1075.62 185.43

19 W50FM6r40 1.4 40 222.52 148.35 742.62 1075.62 185.43

20 W50FM12r40 1.4 40 222.52 148.35 742.62 1075.62 185.43

21 W50FM18r40 1.4 40 222.52 148.35 742.62 1075.62 185.43

22 W50FM25r40 1.4 40 222.52 148.35 742.62 1075.62 185.43

No. Mix ID γFly ash,

%

Proportions of concrete per 1 m3,

Portland

cement type Ifly ashes sand lime stone water

Ref. code: 25605722040416SAT

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3.4.2.2 Compressive strength

To investigate the effect of high LOI fly ash on compressive strength of

concrete, the compressive strength test was conducted in 3 different cases, which are

controlled water to binder ratio, controlled slump by using superplasticizer and

controlled slump by the adjustment of water. Mix proportions of high LOI fly ash

concrete for all cases are shown in Table 3.5. Water to binder ratios of 0.4 and 0.5

were used for the controlled water to binder ratio condition. For controlled slump

conditions, slump of concrete mixture was controlled at 8.5 ± 1 cm for both cases of

using type F naphthalene based superplasticizer and the adjustment of water. Fly

ashes with %LOI of 0, 6, 12, 18 and 25% were used to partially replace cement at

20% and 40% by weight. Moreover, different types of curing, which are water-cured

(WC) and air-cured (AC) conditions, were used to investigate the effect of internal

curing of concrete containing high LOI fly ash.

Cube concrete specimens with dimensions of 100x100x100 mm were used for

compressive strength test. Figure 3.10 shows the molds used to cast the compressive

strength test specimens. Three specimens were prepared for each mixture to obtain the

average compressive strength. Immediately after completion of molding, plastic

sheets were used to cover the top surface of specimens to prevent the moisture loss to

the environment. The specimens were demolded 24 hours after casting and exposed to

the two different curing conditions. All air-cured specimens were kept in a room with

temperature of 28 1C and RH of 75 5%. Compressive strength test was carried

out at the ages of 3, 7, 28 and 91 days by the compressive strength test machine (see

Figure 3.11).

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Figure 3.10 Cube molds having size of 10x10x10 cm for casting concrete

Figure 3.11 Compressive strength test machine

Ref. code: 25605722040416SAT

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Table 3.5 Mix proportions of concrete for compressive strength test.

% kg kg kg kg kg cc cm

1 W40OPC 0.40 - 450.48 0.00 742.62 1075.62 180.19 - 4.8

2 W40FM0r20 0.40 20 347.31 86.83 742.62 1075.62 173.65 - 7.4

3 W40FM6r20 0.40 20 347.31 86.83 742.62 1075.62 173.65 - 4.6

4 W40FM12r20 0.40 20 347.31 86.83 742.62 1075.62 173.65 - 3.6

5 W40FM18r20 0.40 20 347.31 86.83 742.62 1075.62 173.65 - 3.4

6 W40FM25r20 0.40 20 347.31 86.83 742.62 1075.62 173.65 - 1.7

7 W40FM0r40 0.40 40 251.36 167.58 742.62 1075.62 167.58 - 9.0

8 W40FM6r40 0.40 40 251.36 167.58 742.62 1075.62 167.58 - 6.5

9 W40FM12r40 0.40 40 251.36 167.58 742.62 1075.62 167.58 - 4.0

10 W40FM18r40 0.40 40 251.36 167.58 742.62 1075.62 167.58 - 2.5

11 W40FM25r40 0.40 40 251.36 167.58 742.62 1075.62 167.58 - 1.0

12 W50OPC 0.50 - 395.37 0.00 742.62 1075.62 197.69 - 13.0

13 W50FM0r20 0.50 20 306.18 76.55 742.62 1075.62 191.36 - 17.0

14 W50FM6r20 0.50 20 306.18 76.55 742.62 1075.62 191.36 - 15.0

15 W50FM12r20 0.50 20 306.18 76.55 742.62 1075.62 191.36 - 13.5

16 W50FM18r20 0.50 20 306.18 76.55 742.62 1075.62 191.36 - 11.5

17 W50FM25r20 0.50 20 306.18 76.55 742.62 1075.62 191.36 - 9.5

18 W50FM0r40 0.50 40 222.52 148.35 742.62 1075.62 185.43 - 20.5

19 W50FM6r40 0.50 40 222.52 148.35 742.62 1075.62 185.43 - 17.5

20 W50FM12r40 0.50 40 222.52 148.35 742.62 1075.62 185.43 - 15.5

21 W50FM18r40 0.50 40 222.52 148.35 742.62 1075.62 185.43 - 12.0

22 W50FM25r40 0.50 40 222.52 148.35 742.62 1075.62 185.43 - 8.5

23 W40OPC 0.40 - 450.48 0.00 742.62 1075.62 180.19 1441.53 8.0

24 W40FM0r20 0.40 20 347.31 86.83 742.62 1075.62 173.65 0.00 8.5

25 W40FM6r20 0.40 20 347.31 86.83 742.62 1075.62 173.65 651.21 8.2

26 W40FM12r20 0.40 20 347.31 86.83 742.62 1075.62 173.65 1215.58 7.8

27 W40FM18r20 0.40 20 347.31 86.83 742.62 1075.62 173.65 1736.55 8.0

28 W40FM25r20 0.40 20 347.31 86.83 742.62 1075.62 173.65 2257.51 7.6

29 W40FM0r20 0.40 20 347.31 86.83 742.62 1075.62 173.65 - 8.2

30 W40FM6r20 0.44 20 329.60 82.40 742.62 1075.62 181.28 - 8.0

31 W40FM12r20 0.46 20 321.41 80.35 742.62 1075.62 184.81 - 8.0

tested

slump

Case.1 controlled water to binder ratio

%r

fly

ash

Proportions of concrete per 1 m3

Case.2 controlled slump at 8.5 cm by using super plasticizer

Mix IDNo. w/bsuper

plasticizer

Case.3 controlled slump at 8.5 cm by adjusment of water

Portland

cement

type I

fly ashes sand lime stone water

Ref. code: 25605722040416SAT

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3.4.3 Durability of high LOI fly ash concrete

3.4.3.1 Autogenous shrinkage

The purpose of this experiment is to investigate the effect of high LOI fly ash

on autogenous shrinkage. Low to high LOI fly ashes with various %LOI of 0, 6, 12

and 18% were used to replace cement at 20%, by weight. Autogenous shrinkage of

cement and fly ash pastes were evaluated at w/b ratios of 0.25 and 0.4. Details of the

mix proportions are shown in Table 3.6. Paste specimens with dimensions of

25x25x285 mm were used. Figure 3.12 shows the molds used to cast shrinkage test

specimens. A total of 3 specimens were prepared for each mixture. Immediately after

completion of molding specimens, plastic sheets were used to cover the top surface of

specimens to avoid moisture loss to environment. After casting, the specimens were

kept in a controlled environment of 281C. Specimens were demolded at 24 hours

after casting and all of them were sealed by paraffin for the first layer. For the second

layer, specimens were wrapped by plastic sheets. Aluminum foil sheets were used as

the third layer. Figure 3.13 shows the final image of autogenous shrinkage specimens

after the preparation was finished. After that, the Initial length measurement using the

length comparator (Figure 3.14), were then taken on each specimen. The specimens

were kept in the controlled environment of 281C and 755% RH throughout the

experiment. The length change was measured daily for the first two weeks after

demolding and then once a week as the shrinkage rate are stabilized with time. The

autogenous shrinkage measurement was conducted for 91 days.

Figure 3.12 Bar molds for autogenous and total shrinkage test

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Figure 3.13 Autogenous shrinkage paste specimens

Figure 3.14 The length comparator used for measuring the expansion of

bar specimen

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3.4.3.2 Total shrinkage

Total shrinkage is mainly consisted of drying shrinkage and some amount of

autogenous shrinkage. The paste specimens for total shrinkage were prepared with the

same size and mix proportions of autogenous shrinakage. Three specimens were

prepared for each mixture. After completion of molding specimens, plastic sheets

were used to cover the top surface of specimens to avoid moisture loss. Specimens

were placed in a controlled environment of 281C and 755 RH. Specimens were

demolded at 24 hours after casting. All specimens were kept in the same controlled

environment as the autogenous shrinkage specimens (see Figure 3.15). The length

change of specimens was measured by using the length comparator (see Figure 3.14).

The length change was measured daily for the first two weeks after demolding and the

frequency of measurement was once a week as the shrinkage rate is gradually

stabilized with time. The total shrinkage measurement was conducted for 91 days.

Figure 3.15 Bar specimens for total shrinkage test

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Table 3.6 Mix proportions of pastes for autogenous shrinkage and total shrinkage

test.

3.4.3.3 Carbonation

Carbonation depth of cement-only concrete and fly ash concrete having

various %LOI ranges from 0 to 25% were tested in order to investigate the effect of

high LOI fly ash on carbonation resistance of concrete. Fly ash replacement was 20%.

Details of all mix proportions for carbonation test are presented in Table 3.7. The

effect of high LOI fly ash on carbonation was also tested at different water to binder

ratios of 0.4 and 0.5.

Cube concrete specimens having size of 100x100x100 mm were cast and

demolded at 24 hours after casting. Two curing conditions, which are water-cured and

air-cured conditions, were used to cure the concrete specimens for 28 days before

exposing to carbonation. In this study, accelerated carbonation test was selected in

order to shorten the test period. The CO2 subjection environment was controlled such

that the CO2 concentration, the temperature and the relative humidity were 4%

(40,000 ppm), 40±2°C and 55±5%, respectively. After CO2 subjection for 28 and 56

days, specimens were split into half and cleaned. The depth of carbonation was

determined by spraying 1% of phenolphthalein in the solution of 70% ethyl alcohol

FM0 FM6 FM12 FM18

1 W25OPC - 1.00 - - - - 0.25

2 W25FM0r20 20 0.80 0.20 - - - 0.25

3 W25FM6r20 20 0.80 - 0.20 - - 0.25

4 W25FM12r20 20 0.80 - - 0.20 - 0.25

5 W25FM18r20 20 0.80 - - - 0.20 0.25

6 W40OPC - 1.00 - - - - 0.25

7 W40FM0r20 20 0.80 0.20 - - - 0.25

8 W40FM6r20 20 0.80 - 0.20 - - 0.25

9 W40FM12r20 20 0.80 - - 0.20 - 0.25

10 W40FM18r20 20 0.80 - - - 0.20 0.25

fly ashesNo. Mix ID Fly ash, %

Mix proportion(ratio by weight)

Portland

cement type Iw/b

Ref. code: 25605722040416SAT

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[61] on a freshly broken surface. The phenolphthalein solution is colorless but its

color could changes to purple when pH of the concrete specimen is higher than the

range of approximately 9. Therefore, when the solution is sprayed on a broken

concrete surface, the carbonated portion undergoes no color change and the non-

carbonated portion changes to purple (see Figure 3.16). The depth of carbonation is

defined as the thickness of carbonated portion. The carbonation depth was taken as

the average of 12 carbonation depth readings measured from four sides of the broken

surface of the specimens.

Figure 3.16 Specimens after spraying phenolphthalein solution

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3.4.3.4 Rapid Chloride Penetration Test (RCPT)

In this study, chloride resistance was observed in terms of chloride

permissibility. To study the chloride resistance of high LOI fly ash concrete, the

chloride permissibility of cement-only concrete and fly ash concrete having various

%LOI ranges from 0 to 25% were tested by mean of rapid chloride penetration test

(RCPT). Cylinder molds (Figure 3.17) having diameter and height of 100 mm and

200 mm, respectively, were used to cast concrete. After demolding, all the specimens

were cured in the water until the test ages. The RCPT was conducted at the age of 28,

56 and 91 days. At the test ages, each specimen was cut into 3 slices, having a

thickness of 51 ± 3 mm (Figure 3.18). The samples preparation and procedures for

RCPT were performed according to ASTM C1202 [62]. The current was read and

recorded every 30 min using a data logger (Figure. 3.19). The effect of high LOI fly

ash on chloride resistance of concrete was also tested at different water to binder

ratios of 0.4 and 0.5. Fly ash replacement percentage was 20%. Details of all mix

proportions for RCPT test are shown in Table 3.7.

Figure 3.17 Cylinder molds

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Figure 3.18 A slice of RCPT specimen

Figure 3.19 Apparatus for Rapid Chloride Penetration Test

Ref. code: 25605722040416SAT

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Table 3.7 Mix proportions of concrete for carbonation and RCPT test.

kg kg kg kg kg

1 W40OPC 0.4 - 450.48 0.00 742.62 1075.62 180.19

2 W40FM0r20 0.4 20 347.31 86.83 742.62 1075.62 173.65

3 W40FM6r20 0.4 20 347.31 86.83 742.62 1075.62 173.65

4 W40FM12r20 0.4 20 347.31 86.83 742.62 1075.62 173.65

5 W40FM18r20 0.4 20 347.31 86.83 742.62 1075.62 173.65

6 W40FM25r20 0.4 20 347.31 86.83 742.62 1075.62 173.65

7 W40FM0r40 0.4 40 251.36 167.58 742.62 1075.62 167.58

8 W40FM6r40 0.4 40 251.36 167.58 742.62 1075.62 167.58

9 W40FM12r40 0.4 40 251.36 167.58 742.62 1075.62 167.58

10 W40FM18r40 0.4 40 251.36 167.58 742.62 1075.62 167.58

11 W40FM25r40 0.4 40 251.36 167.58 742.62 1075.62 167.58

12 W50OPC 0.5 - 395.37 0.00 742.62 1075.62 197.69

13 W50FM0r20 0.5 20 306.18 76.55 742.62 1075.62 191.36

14 W50FM6r20 0.5 20 306.18 76.55 742.62 1075.62 191.36

15 W50FM12r20 0.5 20 306.18 76.55 742.62 1075.62 191.36

16 W50FM18r20 0.5 20 306.18 76.55 742.62 1075.62 191.36

17 W50FM25r20 0.5 20 306.18 76.55 742.62 1075.62 191.36

18 W50FM0r40 0.5 40 222.52 148.35 742.62 1075.62 185.43

19 W50FM6r40 0.5 40 222.52 148.35 742.62 1075.62 185.43

20 W50FM12r40 0.5 40 222.52 148.35 742.62 1075.62 185.43

21 W50FM18r40 0.5 40 222.52 148.35 742.62 1075.62 185.43

22 W50FM25r40 0.5 40 222.52 148.35 742.62 1075.62 185.43

No. Mix ID w/bFly ash,

%

Proportions of concrete per 1 m3

fly ashes sand lime stone waterPortland

cement

type I

Ref. code: 25605722040416SAT

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3.4.4 Microstructure of high LOI fly ash concrete

3.4.4.1 Porosity of fly ash mortar and concrete

Porosity of mortars and concrete containing low and high LOI fly ash, having

%LOI of 0.77, 6 and 12% were tested according to ASTM C642 [63]. Cube

specimens having dimension of 50x50x50 mm were used to determine the porosity of

mortar and specimens having dimension of 60x60x100 mm were used to determine

the porosity of concrete. Two water-cured specimens were used per each mortar and

concrete mixture to obtain the average void value. The w/b of tested mixtures were

0.25 for fly ash mortar and 0.4 for fly ash concrete. The porosity determination in this

study was carried out at the age of 3 days for mortar and 28 days for concrete.

3.4.4.2 Micro hardness

It has been found by some previous researches that the use of bottom ash or

other light weight aggregate, which are porous materials, form the formation of a hard

shell around their particles and significantly influences the mechanical properties of

the concrete [65-67]. Therefore, micro hardness test on high LOI fly ash concrete was

conducted, since high LOI fly ash is also a porous material.

Micro hardness test was carried out for W40FM0 and W40FM12 mixtures,

which are low w/b fly ash concrete (w/b=0.4) containing fly ashes with LOI of 0.77

and 12%, respectively. Concrete specimens having size of 100x100x100 mm were

cast and cured in water for 28 days. After that they were cut into small cube

specimens having dimension of 10x10x10 mm by a diamond cutter. The small

concrete cubes were then submerged in acetone solution for 24 hours in order to stop

the hydration reaction of cement paste. After that, the specimens were dried, by

keeping it in the oven at 55°C for another 24 hours. Finally, the dried specimens were

put into a vacuum container for 12 hours.

Three concrete cubes having size of 10x10x10 mm were put into a mold (Fig

3.20). Choose the test surface that contains large paste area in order to investigate

micro hardness around fly ash and carbon particles and make sure that the chosen test

surface are attached to the bottom of the mold. The resin solution was made from

Epofix Resin and EpoFix hardener with the ratio of 1:8 by volume. The prepared resin

solution was then poured into the molds under the pressure of 90 kPa for 1 hour. The

Cito Vac instrument was used in order to eliminate the air inside the samples and to

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make the resin solution deeply penetrate into the samples. Next, all molds were kept

in the oven at 50°C and demolded after 24h. After that, the surface of the specimens

and resin were together smoothened by polishing with sand papers No. 120, 220, 500,

800 and 1200, respectively. The final specimen after polishing is shown in Figure

3.21.

In this study, the Vickers hardness test was conducted, following ASTM

C1326 and C1327. In this method, Vickers indenter, made from diamond of specific

geometry, was pressed into the test specimen surface under an applied force of 150gf

using a test machine specifically designed for such work, as seen in Figure 3.22. The

Vickers hardness number is based upon the force divided by the surface area of the

indentation. It is assumed that elastic recovery does not occur when the indenter is

removed. In this study, hardness values at distances of 20 μm to 250 μm from the

boundary of the unburned carbon and fly ash particles were measured.

Figure 3.20 Mold and cube concrete Figure 3.21 Concrete cubes inside resin

specimens after polishing

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Figure 3.22 Vickers hardness test apparatus

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Chapter 4

Results of Basic Properties of High LOI Fly Ash

4.1 General

Artificial high LOI fly ashes were made by mixing low LOI fly ash from Mae-

Moh power plant with a powdered activated carbon (PAC). Chemical compositions of

cement, fly ash and PACs were tested by XRF. In order to make artificial high LOI

fly ash, the information about morphology and surface texture of unburned carbon

particles in fly ash are crucial for making decision on which PACs will be use.

Therefore, Microscopic studies of low and high LOI fly ashes and PACs, were carried

out by Scanning Electron Microscope (SEM). The elemental compositions of fly ash

particles were also tested by Energy Dispersive X-ray (EDX).

4.2 Morphology of fly ashes and powdered activated carbons (PACs)

4.2.1 Morphology of fly ashes with various %LOI

SEM pictures of Mae-Moh fly ash with low LOI content (Figure 4.1) show that

most of its particles are small and big spheres. Some particles with porous and

irregular shape were observed in BLCP fly ash (Figure 4.2), which has %LOI of

5.36%. When %LOI is 18.04%, in case of Vietnamese fly ash (Figure 4.3), there were

plenty of the irregular and porous particles mixing with the fine round spheres.

Majority of the irregular particles, often found in high LOI fly ashes, are believed to

be the unburned carbon particles. Therefore, the EDX test was carried out on some of

the irregular particles. The EDX result of particle #1, as illustrated in Figure 4.4,

demonstrates the high amount of carbon percentage of the particular area tested on

that particle. Hence, it can be said that it is an unburned carbon particle.

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(a) x200

(b) x1000

Figure 4.1 SEM pictures of a low LOI fly ash (LOI= 0.77%)

from Mae-Moh power station, Thailand

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(a) x200

(b) x1000

Figure 4.2 SEM pictures of a high LOI fly ash (LOI = 5.36%)

from BLCP power station, Thailand

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(a) x200

(b) x1000

Figure 4.3 SEM pictures of a high LOI fly ash (LOI=18.04%)

from Vietnam

#1

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Figure 4.4 EDX result of particle #1 (see Figure 4.3a), Vietnamese fly ash

4.2.2 Morphology of Powdered Activated Carbons (PACs)

The PACs in this research were from 3 available sources of activated carbon

in Thailand, which are activated carbon produced from coconut shell, bituminous coal

and wood. The carbon content, tested by LOI test, of the 3 PACs were 85.28%,

86.18% and 80.37% respectively. PAC selection was considered based only on their

physical properties, especially the particle shape by SEM. This is because the

unburned carbon particles are the non-reactive portion of fly ash [68]. Therefore, its

physical properties have more influences on properties of concrete when compared to

its chemical composition. Activated carbon was in the form of granular and powdered

activated carbon. The granular activated carbon were ground to powdered activated

carbon before SEM test. Figures 4.3a to 4.3c show particle shapes of PAC-CS, PAC-

BC and PAC-W by SEM, respectively. Rough texture of PAC-BC and PAC-W were

similar to that of the unburned carbon particles of Vietnamese fly ash (UC-FV) while

PAC-CS has quite smooth surface. However, the shape and pore structure of PAC-W

were totally different from PAC-CS and UC-FV. Therefore, PAC-BC was selected for

preparing artificial high LOI fly ash in this experiment.

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(a) PAC-CS

(b) PAC-BC

(c) PAC-W

Figure 4.5 SEM pictures of Powdered Activated Carbons (PACs)

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4.3 Properties of artificial high LOI fly ash

The selected activated carbon, which is the one produced from Bituminous

coal (PAC-BC), was ground to have similar particle size distribution to the unburned

carbon particles in the Vietnamese fly ash (Figure 4.6). After that the ground activated

carbon or powdered activated carbon (PAC-BC) was thoroughly mixed with Mae-

Moh fly ash by a mixing machine in order to increase LOI of fly ash from 0.77% to

approximately 6%, 12%, 18% and 25%. In this research, these new fly ashes were

called the artificial high LOI fly ashes. Figures 4.7a and 4.7b compare the SEM

images of the real high LOI fly ash from Vietnam with the produced artificial high

LOI fly ash (both having %LOI approximately of 18%). After all the artificial high

LOI fly ashes had been prepared, their basic properties were tested.

Figure 4.6 Particle size distributions of UC-FV and PAC-BC

0

20

40

60

80

100

0.01 0.1 1 10 100 1000

Cum

ula

tive

Pas

sing (

%)

Sieve Size (micron)

Unburned Carbon in Vietnamese fly ash(UC-FV)

Powdered Activated Carbon (PAC-BC)

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a) Real high LOI fly ash from Vietnam (LOI=18.04%)

b) Artificial high LOI fly ash (LOI=18.41%)

Figure 4.7 SEM pictures of real and artificial high LOI fly ashes

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4.3.1 Basic properties of fly ash

It is noted that the actual %LOI in the prepared fly ashes for the tests in this

study are not exactly 0%, 6%, 12%, 18% and 25% but are the values listed in Table

4.1. The values in Table 4.1 are the actually tested LOI of the prepare fly ashes. The

results of tested basic properties of artificial high LOI fly ashes containing various

%LOI ranging from 0.77% to approximately 25% are shown in Table 4.2. When

%LOI of fly ash increases from 0.77% to 25.37%, moisture content also increases

from 0.29 to 2.02. However, the moisture content of all fly ashes, are still lower than

that of the allowable limit in the standard specification, which ASTM C618 limits the

maximum moisture content of fly ash at 3%. Surface area of fly ashes, which can be

approximately determined by Blaine fineness method, increases from 2837 to 3561

cm2/g as the %LOI of fly ash increases from 0.77% to 25.37%. The Specific gravity

of fly ashes decreases from 2.21 to 2.02, showing that high LOI fly ash is lighter than

low LOI fly ash.

Table 4.1 Actual tested %LOI in the prepared fly ashes

Tested fly ash Actual %LOI

FM0 0.77 %

FM6 6.22 %

FM12 12.37 %

FM18 18.41 %

FM25 25.37 %

Table 4.2 Moisture content, specific gravity and Blaine fineness of fly ashes with

various %LOI

Artificial high

LOI Fly ash ID

Moisture

(%)

Specific

gravity

Blaine fineness

(cm2/g)

FM0 0.29 2.21 2837

FM6 0.50 2.16 3038

FM12 1.26 2.12 3164

FM18 1.77 2.07 3388

FM25 2.02 2.02 3561

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4.3.2 Particle size distribution

Particle size distribution results of cement, artificial high LOI fly ash with

various %LOI and PAC produced from bituminous coal were tested by Laser

diffraction technique (see Figure 4.8). The result shows that OPC has the finest

particle size distribution whereas the particle size of PAC is the coarsest. Fly ash with

%LOI of 0.77% has finer particle size distribution than those of high LOI fly ashes.

Particle size distribution of fly ash becomes coarser as the %LOI of fly ash increases.

Nevertheless, since the specific surface area of high LOI fly ash is higher than the low

LOI fly ash while it is coarser, this result is one of the evidences indicating that high

LOI fly ash definitely has a more porous structure.

Figure 4.8 Particle size distributions of cement, fly ashes with various %LOI and

PAC produced from bituminous coal

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4.3.3 Water retainability

Figure 4.9 shows the result of water retainability of fly ashes, which was

tested according to the test method proposed by Tangtermsirikul and Kitticharoeniat

[60] The water retainability of fly ashes gradually increase from 0.18 to 0.35 with the

increase of %LOI of fly ashes from 0.77 to 25.37%. The water retainabilityof fly

ashes having %LOI equal to or higher than 12% were greater than that of OPC. Water

retainability of powder depends on many parameters, such as porosity, environment

temperature, surface condition, shape and size distribution of powder. Considering

physical properties, it was found that restricted water on granular powder is greater

than spherical powder.

Figure 4.9 Water retainability coefficients of fly ashes with various %LOI

0.18

0.22

0.25

0.30

0.35

OPC=0.23

0.00

0.10

0.20

0.30

0.40

0 6 12 18 25

Wat

er r

etai

nab

ilit

y c

oef

fici

ent

LOI of fly ash, %

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4.3.4 Water requirement

Water requirement of mortars containing fly ashes with various %LOI of

approximately 0.77, 12, 18 and 25% are shown in Figure 4.10. In this case, the fly

ash replacement percentage of 20% was used as a cement replacement in the

mixtures. The result shows that only fly ash with LOI of 0.77% requires less water

requirement than the mortar incorporating only cement. It can be obviously seen that

as %LOI of fly ash increases from 0.77 to 25.37%, water requirement of mortars also

gradually increases from 97.12 to 104.39%.

Figure 4.10 Water requirement of mortars containing fly ashes with various %LOI

100.00

97.12

100.68

102.78 104.39

80

85

90

95

100

105

110

OPC

FMr2

0

FM12

r20

FM18

r20

FM25

r20

Wat

er r

equir

emen

t, %

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Chapter 5

Results and Clarifications of Slump

5.1 Initial slump of concrete

The initial slump of concrete mixtures was tested at water to binder ratios of 0.4

and 0.5 (see Figures 5.1 and 5.2, respectively). Fly ashes having various %LOI were

used as a cement replacement at 20% and 40% (by weight). It can be obviously seen

from the results that fly ash mixture with the lowest %LOI (LOI= 0.77%) has the

highest slump. In case of w/b of 0.4 (see Figure 5.1), when %LOI of fly ash increases

from 0.77 to 25.37%, slump of fly ash concrete gradually decreases from 7.4 cm to

1.7 cm (%r=20%) and 9.0 cm to 1.0 cm (%r=40%). For mixtures of w/b of 0.5 (see

Figure 5.2), when %LOI of fly ash increases from 0.77 to 25.37%, slump of fly ash

concrete also gradually decreases from 17.0 cm to 9.5 cm (%r=20%) and 9.0 cm to

1.0 cm (%r=40%).

It can be said that the higher the LOI percentage of fly ash is, the more the

slump of fly ash concrete is reduced for all w/b ratios and fly ash replacement

percentages, due to the irregular shape and porous characteristic of the high LOI fly

ash particles. However, slump of mixtures containing fly ash having %LOI lower or

equal to 6% in case of w/b ratio of 0.4 (see Figure 5.1) and 12% in case of w/b ratio

of 0.5 (see Figure 5.2), can be higher or equal to the slump of OPC mixtures when fly

ash were replaced at 20%. These results correspond to the limitation of %LOI in

ASTM or many other countries’ standards, which mostly limit the maximum %LOI of

fly ash using in concrete at about 6%.

Increasing fly ash content in the mixtures from 20% to 40% replacement greatly

improves the workability of fresh concrete for mixtures containing fly ash that has

%LOI lower or equal to 6% (in case of w/b ratio = 0.4) and 12% (in case of w/b ratio

= 0.5). As the slump of fly ash concrete gradually decreases with the increase of

%LOI of fly ash, increasing the replacement percentage of fly ash that has %LOI

greater than 12% in the mixtures adversely affects the slump by decreasing the slump

of concrete even more. It can be observed from Figures 5.1 and 5.2 that the lines of

fly ash replacements of 20% and 40% intersect at a certain %LOI of the fly ash,

meaning that, using not too high LOI fly ashes, higher fly ash replacement offers

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better slump performance. On the other hand, when very high LOI fly ashes are used,

higher fly ash replacement can lead to a lower slump performance. This behavior will

be explained in the section 5.2.

Figure 5.1 Initial slump of concrete containing fly ashes with various %LOI

(w/b = 0.4)

Figure 5.2 Initial slump of concrete containing fly ashes with various %LOI

(w/b = 0.5)

OPC=4.8

0

2

4

6

8

10

0 6 12 18 25

Init

ial

Slu

mp (

cm)

LOI of fly ash, %

r20 r40

OPC=13

0

5

10

15

20

25

0 6 12 18 25

Init

ial

Slu

mp (

cm)

LOI of fly ash, %

r20 r40

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5.2 Clarification of slump behavior

It was found that the higher the LOI percentage of fly ash, the more slump of fly

ash concrete is reduced for all tested w/b ratios (0.4 and 0.5). Moreover, increasing fly

ash content in the mixtures from 20% to 40% replacement improves the workability

of fresh concrete for mixtures containing fly ash having %LOI lower or equal to 12%.

On the contrary, the slump of fly ash mixture, having %LOI higher than 12%,

gradually decrease with the increase of fly ash replacement percentage. This

phenomenon created the intersection between the lines of two replacement

percentages of fly ash. The reasons for the intersection of slump graphs discussing

before, were explained by adopting the slump prediction model, which describes the

relationship between the effect of water retainability and the lubrication effect of fly

ash. In this segment, slump prediction model [69] will be employed to explain the

slump behavior of the fly ash concrete.

5.2.1 Background of slump model

Model for predicting workability of fresh concrete was proposed by

Tangtermsirikul et al [69] are shown in Eq (5.1).

SL = α(Wfr − W0) (5.1)

where Wfr is volume of free water in the fresh concrete mixture (kg/m3 of concrete),

W0 is the minimum free water content required initiating slump (kg/m3 of concrete), α

is the slope of slump-free water content curve (cm/kg/m3 of concrete), and SL is

slump value of fresh concrete (cm).

5.2.1.1 Slope of slump-free water content curve (𝛂)

It was found that slopes of the slump-free water content curves increased with

the increase of ratio between paste volume and void content of compacted aggregate

phase (). It is noted here that some effect of aggregate properties are indirectly

considered by, such as gradation and aspect ratio. The ratio of paste volume to void

content of compacted aggregate phase is defined as:

γ =

Vp

Vvoid (5.2)

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where Vp is the volume of paste in the unit volume (1 m3) of fresh concrete and Vvoid

is the volume of void in the densely compacted total aggregate (fine and coarse

aggregate) in the unit bulk volume (1 m3) of aggregate. The volume of paste can be

derived as:

Vp = Vc + Vw + Vair + Vpow (5.3)

where Vc, Vw, Vair and Vpow are the volume of cement, water, air and other powder

materials, respectively, in a unit volume (1 m3) of concrete mixture.

The relationship between slope of slump-free water content curve () and

value of was found from the analysis of experimental data as shown in Eq. (5.4).

α = 3.57γ4 − 21.34γ3 + 46.74γ2 − 43.92γ + 14.94 (5.4)

5.2.1.2 Free water content in fresh concrete (Wfr)

Free water means the amount of water that is free, by any means, from being

restricted by all solid particles in the fresh concrete and can be obtained from unit

water content minus water retainability of powder materials and surface water

retainability of aggregates as:

Wfr = Wu − Wrp − Wra′ (5.5)

where Wu is the unit water content in the mixture (kg/m3 of concrete), Wrp is the

restricted water by powder materials (kg/m3 of concrete), and Wra′ is the restricted

water at the surface of aggregates (kg/m3 of concrete).

(1) Water retainability of powder materials (𝛃𝒑)

The total amount of restricted water by all powder materials can be

derived from the summation of the product between the weight of each

powder and its water retainability.

Wrp = ∑ β𝑝𝑖𝑤𝑝𝑖

𝑛

𝑖=1

(5.6)

where β𝑝𝑖 is the water retainability coefficient of powder material type i which

is obtained from the tested water retainability coefficient results in chapter 4,

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w𝑝𝑖 is the absolutely dried weight of powder material type I (kg/m3 of

concrete), n is total number of powder materials used in the concrete.

(2) Surface water retainability of aggregates (𝐖𝐫𝐚′ )

In mix design of concrete, unit water content does not include the

absorption of aggregates. So the restricted water in addition to the absorbed

water in the aggregate particles is considered here. The surface water

retainabilithy of aggregates can be expressed as:

Wra′ = βs

′ ws′ + βg′wg′ (5.7)

where , βs′ , βg′ are the surface water retainability coefficients (excluding

absorption) of fine and coarse aggregates, respectively, and ws′ , wg′ are

saturated surface dried weights of sand and gravel respectively (kg/m3 of

concrete).

(a) Water retainablity coefficient of aggregates (𝛃𝐚𝐠𝐠′)

It was assumed that the water retainability of aggregates depends

on irregularity and size of the particles so that specific surface area can

be considered an appropriate parameter. The derived surface water

retainability coefficient of aggregates including sand and gravel is as

follow.

βagg′ = 2 × 10−6(Sagg)0.9

(5.8)

where βagg′ is the surface water retainability coefficient (excluding

absorption) of aggregate (g/g of SSD aggregate) and Sagg is specific

surface area of aggregate (cm2/kg). in practice, the water retainability

of coarse aggregate can be neglected due to its small value when

compared to that of the fine aggregate.

(b) Determination of specific surface area of fine and coarse

aggregates

In this study, a calculation method was used to compute surface

area of aggregate by first assuming that the shape of aggregate particle is

spherical. The specific surface area of aggregate on spherical shape basis

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can be calculated from the gradation as expressed in the following

equation.

So =

6000

Dav × ρ (5.9)

Dav =

∑ D𝑖𝑀𝑖

∑ M𝑖 (5.10)

where S0 is the specific surface area of aggregate on spherical shape

basis (cm2/g), Dav is the average diameter of the aggregate particles

(cm), Di is the average dimension between the upper sieve and the sieve

i on which aggregate particles are retained (cm), Mi is the percentage of

retaining on the corresponding sieve of the aggregate group i, (%), and ρ

is the specific gravity of the aggregate.

Then angularity factor is applied to account for the irregularity of

the particles. As the result, the specific surface area of irregular

aggregate can be estimated by multiplying the angularity factor to the

specific surface area of the assumed spherical aggregate, that is

calculated from sieve analysis as:

Sg = ψg × Sgo (5.2)

Ss = ψs × Sso (5.3)

Where Ss and Sg are the specific surface area of irregular fine and coarse

aggregates, respectively (cm2/g). ψs and ψg are the angularity factors of

fine and coarse aggregates, respectively. Sso and Sgo are the specific

surface area of the assumed spherical fine and coarse aggregates,

respectively (cm2/g).

5.2.1.3 Minimum free water content required to initiate slump (Wo)

The interparticle surface forces vary with the numbers of feasible interparticle

contact among the solid particles, and particles with the larger surface are result in

more contacts. As the result, the interparticle surface forces can be considered to vary

with the surface area of the solid particles that have possibility to be in contact, which

is defined in this study as effective surface area (Seff, cm2/m3 of concrete). Then, the

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amount of water for balancing these interparticle surface forces (Wo) can be expressed

as a function of Seff.

It is well known that spherical fillers can reduce interparticular friction among

larger particles, i.e. cement-to-cement, cement-to-aggregate, and aggregate-to-

aggregate frictions. This effect is identified as lubrication effect. Lubrication is

thought to reduce friction and therefore Wo. The lubrication coefficient (L) was

introduced to account for lubrication effect of spherical-shape powder. The empirical

equation for Wo was derived as:

Wo = [8 × 10−5(Seff)0.70]/L (5.4)

1) Effective surface area of solid particles (𝐒𝐞𝐟𝐟)

The effective surface area of solid particles indicates the possible

contacts among the fine aggregates, coarse aggregate and powder. It was

derived as in the following equation.

Seff = Stagg + η(Spow) (5.5)

Spow = 1000 ∑ Spiwpi

n

i=1

(5.6)

Stagg = 1000(Ssws + Sgwg) (5.7)

where Stagg and Spow are surface area of total aggregates and total powder

materials in concrete, respectively (cm2/m3 of concrete) ws, wg, and wpi are the

saturated surface dried weight of fine aggregate coarse aggregate, and the

absolutely dried weight of powder material type I, respectively (kg/m3 of

concerete). Ss, Sg, and Spi are the specific surface area of fine aggregate,

coarse aggregate, and powder material type I, respectively (cm2/g). n is total

number of powder material used in the concrete. η is the effective contact area

ration indicating the ratio of surface area of powder material, which is

effectively contact around aggregates, which was derived as:

η = 0.026e−3×10−8(Stagg) (5.8)

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2) Lubrication coefficient (L)

The major parameters that affect this coefficient were considered to be

the ratio of specific surface area of powder to specific surface area of cement

and replacement ratio. This is because finer powders are more efficient than

coarser powders in lubrication, and more amount of powder is also more

effective. The shape factor was introduced to incorporate the effect of particle

shape on the lubrication effect by considering that granular particles will have

no lubrication effect whereas spherical particles will have perfect lubrication.

So, the equation for lubrication effect was derived as:

L = 1 + bRc(1.4 − φ) (5.9)

where b = −8.35r2 − 0.24r + 0.19 (5.10)

c = −15.6r2 + 6.0r + 0.5 (5.20)

where R is the ratio of specific surface area of powder to specific surface area

of cement, φ is angularity factor obtained from back calculation and r is

replacement ratio of fly ash.

5.2.2 Verification of initial slump of high LOI fly ash concrete

The tested slump results of fly ash concrete with various LOI percentages, water

to binder ratios and fly ash replacement percentages were compared with the

predicted slump calculated from the proposed model. Both the tested slump and

predicted slump values of fly ash concrete with w/b ratios of 0.4 and 0.5 are shown in

Tables 5.1 and 5.2, respectively. The tested initial slump results obtained from initial

slump test in section 5.1 are shown in Figures 5.1and 5.2 respectively. The predicted

slump results obtained from the slump model are shown in Figures 5.3 and 5.4, for

w/b of 0.4 and 0.5, respectively.

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Table 5.1 Tested and predicted slump results of fly ash concrete containing various

%LOI (w/b =0.4)

w/b %r

LOI, Tested Predicted Error

% (cm) (cm) cm %

0.4

20

0 7.4 5.2 2.2 29

6 4.6 4.4 0.2 4

12 3.6 3.8 -0.2 -5

18 3.4 2.8 0.6 18

25 1.7 1.7 0.0 -1

40

0 9.0 7.7 1.3 14

6 6.5 6.1 0.4 6

12 4.0 4.8 -0.8 -20

18 2.5 2.8 -0.3 -11

25 1.0 0.7 0.3 33

Table 5.2 Tested and predicted slump results of fly ash concrete containing various

%LOI (w/b =0.5)

w/b %r

LOI, Tested Predicted Error

% (cm) (cm) cm %

0.5

20

0 17.0 11.9 5.1 30

6 15.0 11.2 3.8 25

12 13.5 10.6 2.9 21

18 11.5 9.7 1.8 15

25 9.5 8.8 0.7 7

40

0 20.5 14.2 6.3 31

6 17.5 12.7 4.8 27

12 15.5 11.6 3.9 25

18 12.0 9.8 2.2 19

25 8.5 7.9 0.6 7

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The predicted slump results obtained from the slump model were quite

accurate, especially for the predicted slump of those high LOI fly ash mixtures. The

intersection between the lines of two replacement percentages of fly ash, which are

20% and 40%, were also obtained in the predicted slump graph (see Figures 5.3 and

5.4). The reason for these intersection points could be due to the opposite influences

of water retainability and lubrication effect of the high LOI fly ashes. As we can see

that the water retainability is involved in the amount of free water content (Wfr) of a

mixture as shown in equations (5.5) and (5.6). Lubrication effect is involved in the

minimum water content required to initiate the slump of fresh concrete (Wo) as shown

in equation (5.13). The water retainability and lubrication coefficients are shown in

Figures 5.5 and 5.6, respectively. The relationship between Wfr and Wo and %LOI of

fly ash are shown in Figure 5.7. It was found from Figures 5.5 to 5.7 that when LOI

increases, water retainability also increases causing lower free water content (Wfr) and

so lowering the slump of concrete. Lubrication effect helps to reduce the minimum

water content required to initiate slump (W0) and happens only on fly ash at low LOI,

because granular particles will have no lubrication effect whereas spherical particles

will have perfect lubrication. So, when %LOI of fly ash increases, the increase in

granular and porous particles of fly ash lowers its lubrication effect and finally

resulting in high W0. Higher W0 lowers free water of the mixture. Therefore,

increasing replacement percentage of high LOI fly ash will further decrease the slump

of concrete because of both the reduction of free water content (Wfr) due to the

increase in water retainability and the increasing of W0 due to the lowering of

lubrication effect of high LOI fly ash. More vigorous influence on slump when

increasing fly ash replacement percentage is on the reduction of free water (Wfr) due

to increase of %LOI as can be seen from Figure 5.7. Figure 5.7 shows that when

%LOI fly ash replacement is 40%, the slope of the Wfr curve becomes much steeper

when compared to that of the 20% fly ash replacement while the slopes of the W0

curves of both 20% and 40% fly ash replacements are not much different.

Ref. code: 25605722040416SAT

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Figure 5.3 Predicted slump of fly ash concrete with various %LOI

(w/b = 0.4)

Figure 5.4 Predicted slump of fly ash concrete with various %LOI

(w/b = 0.5)

0

2

4

6

8

10

0 6 12 18 25

Init

ial

Slu

mp (

cm)

LOI of fly ash, %

r20

r40

0

5

10

15

20

25

0 6 12 18 25

Init

ial

Slu

mp (

cm)

LOI of fly ash, %

r20

r40

Ref. code: 25605722040416SAT

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Figure 5.5 Water retainability coefficients of fly ashes

with various %LOI

Figure 5.6 Lubrication coefficients of fly ashes

with various %LOI

0.18

0.220.25

0.3

0.35

0.00

0.10

0.20

0.30

0.40

0 6 12 18 25

Wat

er r

etai

nab

ilit

y c

oef

fici

ent

%LOI of fly ash

1.145

1.150

1.155

1.160

1.165

1.170

1.175

0 6 12 18 25

Lub

rica

tion

coef

fici

ent

%LOI of fly ash

Ref. code: 25605722040416SAT

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Figure 5.7 Relationship between Wfr, W0 and %LOI of fly ash

(w/b =0.4)

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

0 6 12 18 25

Volu

me

of

free

wat

er (

Wfr)

and W

0

(kg/m

3)

LOI of fly ash, %

Wfr (r20) W0 (r20)

Wfr (r40) W0 (r40)

Ref. code: 25605722040416SAT

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Chapter 6

Results and Clarifications of Compressive Strength

6.1 General

Compressive strength of high LOI fly ash concrete were tested in controlled

slump and controlled water to binder ratio conditions. The effect of fly ash content

was also tested, by using 2 fly ash replacement percentages, which are 20% and 40%

by weight of the total binders. Moreover, different type of curing conditions, which

are water curing and air curing, were also used to test curing sensitivity of high LOI

fly ash concrete. Then, microstructure of high LOI fly ash concrete was investigated

in order to explain the compressive strength results.

6.2 Effect of high LOI fly ash on compressive strength of concrete

6.2.1 Controlled slump

This section presents the effect of high LOI fly ash on compressive strength of

concrete in controlled slump condition. Slump of concrete was controlled at 8.5 ± 1

cm by 2 methods, adjustment of water and use of type F naphthalene based

superplasticizer. Replacement percentage of fly ash was maintained at 20%. All

mixtures were cured in water until the test ages of 3, 7, 28, 91 days.

The compressive strength of fly ash concrete, in case of controlled slump by

adjustment of water (see Figure 6.1), gradually decreases with the increase of %LOI

of fly ash for all tested ages. In case of controlled slump by the use of superplasticizer

(Figure 6.2), when %LOI is increased up to 12%, compressive strength of fly ash

concrete at early-age tends to increase with the increase of %LOI of fly ash. Then it

gradually decreases with the increase of LOI when %LOI of fly ash is beyond 12%.

Long-term compressive strength of all high LOI fly ashes were comparable to low

LOI fly ash (LOI=0.77%). These results are quite different when compared to most of

the previous findings [15],[47],[49] which found that the increase of %LOI of fly ash

results in low compressive strength.

Ref. code: 25605722040416SAT

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Figure 6.1 Compressive strength of fly ash concrete containing various %LOI

(controlled slump by adjustment of water)

Figure 6.2 Compressive strength of OPC and fly ash concrete containing various

%LOI (controlled slump concrete by using superplasticizer)

40 3835

4844

41

59

5250

64 6260

0

10

20

30

40

50

60

70

80

FM0 FM6 FM12

Com

pre

ssiv

e S

tren

gth

(M

Pa)

Mix ID

3 days 7 days 28 days 91 days

37

27

3033 32 31

53

4648 49 48 48

61

56 57 58 57 56

69 71 71 7169 68

0

10

20

30

40

50

60

70

80

W400PC W40FM0 W40FM6 W40FM12 W40FM18 W40FM25

Com

pre

ssiv

e S

tren

gth

(M

Pa)

Mix ID

3 7 28 91

Ref. code: 25605722040416SAT

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6.2.2 Controlled water to binder ratio

Compressive strength of high LOI fly ash was also tested in controlled water to

binder conditions at w/b ratios of 0.4 and 0.5 as shown in Figures 6.3 and 6.4,

respectively.

The results were similar to compressive strength of controlled slump by the use

of superplasticizer case. Compressive strength of fly ash concrete tends to increase

with the increase in %LOI of fly ash for both tested w/b ratios (0.4 and 0.5). Although

the compressive strength of fly ash concrete tends to decrease when %LOI of fly ash

is beyond 12%, The overall compressive strength of high LOI fly ash concrete are

comparable to the low LOI fly ash (LOI=0.77%). In fact, long-term compressive

strength of high LOI fly ash mixture, having %LOI of 12% for w/b ratio of 0.4, is

even higher than those of the low LOI fly ash and OPC mixtures.

Ref. code: 25605722040416SAT

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52

4042 44 44 44

54

47 4850

4745

62 62 62 6461 61

6668 69

7169

67

0

10

20

30

40

50

60

70

80

W40OPC W40FM0 W40FM6 W40FM12 W40FM18 W40FM25

Com

pre

ssiv

e S

tren

gth

(M

Pa)

Mix ID

3days 7days 28days 91days

31

26 26 27 2728

37

32 3234 35

37

4441 42

43 4341

5249 50 51 50 49

0

10

20

30

40

50

60

70

80

W50OPC W50FM0 W50FM6 W50FM12 W50FM18 W50FM25

Com

pre

ssiv

e S

tren

gth

(M

Pa)

Mix ID

3days 7days 28days 91days

Ref. code: 25605722040416SAT

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6.3 Effect of fly ash content on compressive strength of high LOI fly ash

concrete

This section presents the effect of high LOI fly ash on compressive strength of

concrete with different replacement percentages of fly ash at ages of 3, 7, 28 and 91

days. The effect of fly ash content was investigated for w/b of 0.4 and 0.5 as shown in

Figures 6.5 and 6.6, respectively. Cement was partially replaced with fly ash, with

%LOI ranges from 0.77% to 25.37% by weight, at 20% and 40%. All mixtures were

cured in water till the test ages. Compressive strength of fly ash concrete tends to

increase when LOI increase up to about 12%. Decreasing in compressive strength was

found when the LOI of fly ash is beyond 12%. However, compressive strength of

mixtures with %LOI of 6%, 12%, 18% and 25% are nearly the same as the mix with

the lowest %LOI, which is 0.77%. Mixture with the fly ash having %LOI of 12.37%

seems to have the highest compressive strength for every replacement percentage.

Ref. code: 25605722040416SAT

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a) 3 days b) 7 days

c) 28 days d) 91 days

Figure 6.5 Compressive strength of low and high LOI fly ash concrete

with various %replacement of 20 and 40% (w/b = 0.4)

OPC= 52

0

10

20

30

40

50

60

70

80

0 6 12 18 25

Co

mpre

ssiv

e S

tren

gth

(M

Pa)

LOI of fly ash, %

r 20 r 40

OPC=5

4

0

10

20

30

40

50

60

70

80

0 6 12 18 25

Co

mpre

ssiv

e S

tren

gth

(M

Pa)

LOI of fly ash, %

r 20 r 40

OPC=6

2

0

10

20

30

40

50

60

70

80

0 6 12 18 25

Co

mpre

ssiv

e S

tren

gth

(M

Pa)

LOI of fly ash, %

r 20 r 40

OPC=66

0

10

20

30

40

50

60

70

80

0 6 12 18 25

Co

mpre

ssiv

e S

tren

gth

(M

Pa)

LOI of fly ash, %

r 20 r 40

Ref. code: 25605722040416SAT

78

a) 3 days b) 7 days

c) 28 days d) 91 days

Figure 6.6 Compressive strength of low and high LOI fly ash concrete

with various %replacement of 20 and 40% (w/b = 0.5)

OPC=3

1

0

10

20

30

40

50

60

70

80

0 6 12 18 25

Co

mpre

ssiv

e S

tren

gth

(M

Pa)

LOI of fly ash, %

r20 r40

OPC=3

7

0

10

20

30

40

50

60

70

80

0 6 12 18 25

Co

mpre

ssiv

e S

tren

gth

(M

Pa)

LOI of fly ash, %

r20 r40

OPC=4

4

0

10

20

30

40

50

60

70

80

0 6 12 18 25

Co

mpre

ssiv

e S

tren

gth

(M

Pa)

LOI of fly ash, %

r20 r40

OPC=5

2

0

10

20

30

40

50

60

70

80

0 6 12 18 25

Co

mpre

ssiv

e S

tren

gth

(M

Pa)

LOI of fly ash, %

r20 r40

Ref. code: 25605722040416SAT

79

6.4 Effect of different curing conditions on compressive strength of high LOI fly

ash concrete

Two curing conditions, water-cured (WC) and air-cured (AC) conditions, were

used to evaluate the effect of high fly ash in different curing condition. Fly ash was

used to replace cement at 20% by weight. Compressive strength was tested at two

ages, which are 28 days and 91 days.

6.4.1 Controlled water to binder

In this section, compressive strength of concrete were tested in controlled w/b

at 0.4. Figures 6.7a and 6.7b illustrate the compressive strength of high LOI fly ash

concrete in different curing conditions at 28 and 91 days, respectively. The dotted line

represents compressive strength of OPC concrete in water-cured condition. As

expected air-cured concrete shows lower compressive strength comparing to water-

cured concrete for every LOI level of fly ash. For water-cured concrete, compressive

strength of all fly ash mixtures having various %LOI were comparable to that of OPC

mixture at 28 days, but then higher at 91 days. While the compressive strength of all

fly ash mixtures of air-cured concrete were lower than OPC mixture at both 28 and 91

days. However, the increases in compressive strength are found in both type of curing

conditions. When LOI increases from 0.77% up to 12.37%, compressive strength also

gradually increases. After that, the decreases in compressive strength is found when

LOI level of fly ash is beyond 12%.

a) 28 days b) 91 days

Fig 6.7 Compressive strength of low and high LOI fly ash concrete

in different curing conditions ( controlled w/b at 0.4)

OPC=6

2

50

55

60

65

70

0 6 12 18 25

Co

mpre

ssiv

e S

tren

gth

(M

Pa)

LOI of fly ash, %

W40 (WC) W40 (AC)

OPC=6

6

55

60

65

70

75

0 6 12 18 25

Co

mpre

ssiv

e S

tren

gth

(M

Pa)

LOI of fly ash, %

W40 (WC) W40 (AC)

Ref. code: 25605722040416SAT

80

6.4.2 Controlled slump by using superplasticizer

The effect of high LOI fly ash on compressive strength of concrete in different

curing condition was also tested in the condition such that slump of concrete was

controlled at 8.5 ± 1 cm by the use of superplasticizer. As illustrated in Figures 6.8a

and 6.8b, the results show the same tendency as the controlled w/b ratio case. Air-

cured concrete shows lower compressive strength than the water-cured concrete. The

effect of curing type on compressive strength of fly ash concrete can be clearly seen at

91 days. Concrete with %LOI of 12% demonstrates the highest compressive strength

in both water-cured and air-cured conditions. It should be noted here that the tested

compressive strength of the controlled OPC mixture in this section are slightly

different from those in the section 6.4.1(controlled water to binder) because they were

separately prepared.

a) 28 days b) 91 days

Fig 6.8 Compressive strength of low and high LOI fly ash concrete

in different curing conditions (controlled slump by using superplasticizer)

OPC=6

1

50

55

60

65

70

0 6 12 18 25

Co

mpre

ssiv

e S

tren

gth

(M

Pa)

LOI of fly ash, %

WC AC

OPC=6

9

55

60

65

70

75

0 6 12 18 25

Co

mpre

ssiv

e S

tren

gth

(M

Pa)

LOI of fly ash, %

WC AC

Ref. code: 25605722040416SAT

81

6.5 Curing sensitivity of high LOI fly ash concrete on compressive strength

The curing sensitivity of high LOI fly ash concrete on compressive strength

was evaluated by using the curing sensitivity index (CSIfc′) which is the percentage

difference between compressive strength of concrete that is continuously water-cured

and that of the continuously air-cured concrete as shown in equation (6.1). The higher

curing sensitivity index means concrete is more sensitive to curing. Since concrete

with high w/b is more sensitive to curing because the water loss due to evaporation is

easier when compare to the low w/b mixture. Thus, only curing sensitivities of low

w/b mixtures, which are controlled water to binder ratio concrete (w/b =0.40) and

controlled slump concrete at 8.5 ± 1 cm by the use of superplasticizer, were

investigated.

%, CSIf′c =fc′(WC) − fc′(AC)

fc′(WC)× 100 (6.1)

where CSIf′c is curing sensitivity index for compressive strength(%). fc′(WC) and

fc′(AC) are compressive strength of water-cured and air-cured specimens, respectively

(MPa).

It can be seen from Figures 6.9 and 6.10 that at the age of 28 days, CSIf′c of fly

ash concrete decreases when the %LOI of fly ash increases from 0.77 to 12% but then

start to increase again when %LOI of fly ash is greater than 12%. While CSIf′c at 91

days, gradually decreases until %LOI of fly ash increases up to 18%. It was found that

fly ash with the lowest %LOI (LOI=0.77%) has the highest CSIfc′ at both 28 days and

91 days for both cases, controlled w/b ratio (Fig 6.9) and controlled slump concrete

(Fig 6.10). The lowest CSIf′c was obtained in the mixture containing fly ash with

%LOI of 12% for concrete at 28 days and 18% for concrete at 91 days.

It is a common known that the CSIf′c of fly ash concrete is higher than that

OPC concrete. A study by Kinaanath Hussain [64] found that fly ash increases the

sensitivity of curing due to its slow reaction and it needs water for the pozzolanic

reaction process at long-term age. Another reason is that the rate of evaporation of fly

ash concrete is higher than cement-only concrete so early water loss by evaporation in

Ref. code: 25605722040416SAT

82

air-cured fly ash concrete results in less water inside the concrete for pozzolanic

reaction [65]. At low w/b there is not enough water inside concrete and porosity of the

concrete is low, thus it is difficult for external water to penetrate into the concrete.

The result in this study indicates that high LOI fly ash is capable of reducing the

CSIf′c of fly ash concrete by its potential of internal curing ability. However, it should

be noted that too high percentage of LOI of fly ash could adversely affect the CSIf′c of

fly ash concrete as well as its compressive strength. From the discussion above, the

increase in compressive strength of high LOI fly ash might also be due to this internal

curing effect.

Fig 6.9 Curing sensitivity of fly ash concrete containing various %LOI

for controlled w/b case (w/b= 0.4)

12.88

7.69 7.06

9.55 10.38

14.13

11.75 10.95

10.20 10.15

0

5

10

15

20

FM0 FM6 FM12 FM18 FM25

CS

I fc'

(%

)

MIX ID

28days 91days

Ref. code: 25605722040416SAT

83

Fig 6.10 Curing sensitivity of fly ash concrete containing various %LOI

for controlled slump at 8.5 cm by using admixture case

6.6 Microstructure study of high LOI fly ash concrete

In this part, some microstructure investigations were carried out in order to

find out the possible reasons or evidences to explain the increase in compressive

strength of high LOI fly ash concrete.

6.6.1 Porosity of fly ash mortars and concrete with different %LOI

Porosity of mortar and concrete containing fly ashes with various %LOI were

measured in term of total volume of permeable voids according to ASTM C642. The

total volume of permeable voids of fly ash mortar and concrete specimens, having

various %LOI of 0.77, 6 and 12%, were tested at water to binder ratio of 0.25 and 0.4,

respectively. Test was carried out at the age of 3 days for mortar specimens and 28

days for concrete specimens. Results of volume of permeable voids of the mortar and

concrete specimens are shown as illustrated in Figures 6.11 and 6.12, respectively. It

was found that higher %LOI of fly ash tends to slightly increase the total volume of

permeable voids of mortar or concrete.

The increase in porosity of high LOI fly ash can be one of the reasons that

support the increase in carbonation depth and the reduction in chloride resistance of

high LOI fly ash concrete. However, the increase in porosity of high LOI fly ash

3.89

2.07 1.89 2.13

3.94

14.76

11.81

10.04 9.16

9.77

0

5

10

15

20


CS

I fc'

(%

)

MIX ID

28days 91days

Ref. code: 25605722040416SAT

84

seems to conflict with the increase in compressive strength of high LOI fly ash

concrete.

Figure 6.11 Total volume of permeable voids in fly ash mortars

with different %LOI at the age of 3 days

Figure 6.12 Total volume of permeable voids in fly ash concrete

with different %LOI at the age of 28 days

16.35 16.59 16.68

0

2

4

6

8

10

12

14

16

18

20

FM0 FM6 FM12

Vo

lum

e o

f per

mea

ble

vo

id (

%)

Mix ID

11.34 11.44 11.59

0

2

4

6

8

10

12

14

FM0 FM6 FM12

Vo

lum

e o

f per

mea

ble

vo

id (

%)

Mix ID

Ref. code: 25605722040416SAT

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6.6.2 Microstructure examination of high LOI fly ash concrete by SEM

Use of lightweight aggregates (LWA), which are porous materials, can

improve the interfacial transition zone (ITZ) of concrete by the formation of a dense

ITZ and thus enhances the concrete strength. Lightweight aggregates have high

absorption which can subsequently release water to increase the hydration degree of

the paste around the aggregates, making the paste to develop a structure with low

porosity [76][77]. Wasserman & Bentur [67] also added that for lightweight

aggregates of equal strength, the aggregate of higher absorption would provide higher

strength concrete due to its denser ITZ. Moreover, a study by Lo et al [78], which

used the sintered lightweight aggregate manufactured from high-carbon fly ash, also

found that cement paste infiltrated into the high-carbon fly ash light-weight aggregate

shell (see Figure 6.13), which can provide effective mechanical interlocking between

the light-weight aggregate and the cement paste at the ITZ.

(a) BSEI showing the penetration of cement paste into the HCFA-LWA surface

(x200)

Ref. code: 25605722040416SAT

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(b) Typical view of the HCFA-LWA/cement paste ITZ (x2000) after loading

Figure 6.13 ITZ microstructure of High-carbon fly ash lightweight aggregate

concrete, Lo et al (2016)

Investigation on the microstructure of high LOI fly ash concrete specimen was

carried out using scanning electron microscope (SEM). SEM pictures of fly ash and

carbon particles in polished surface are shown in Figures 6.14 and 6.15. In the

pictures, fly ash particles are white grey sphere particles, while carbon particle are the

black particles. It can be observed from the Figures 6.14 and 6.15 that the cement

paste infiltrated into the rough surface and pores of the carbon particles. This result is

similar to the microstructure of concrete using lightweight aggregate discussed above.

Cement might react with the additional water, absorbed by the carbon particles,

resulting in better bonding between cement and carbon particles and therefore, might

be one reason to not reducing the compressive strength of high LOI fly ash concrete,

in addition to the strength enhancing effect of hardshell formation contributed by

internal curing, that will be proven in the next section.

Ref. code: 25605722040416SAT

87

Figure 6.14 Typical view of paste around a particle of fly ash and carbon

Figure 6.15 ITZ microstructure of a carbon particle and cement paste

Project 1 6/9/2017 11:22:23 AM

Comment:

50µm Electron Image 1

FeFe

Fe K

S

Mg

Al

Si

Ca

Ca

O

K

C

0 2 4 6 8 10 12 14 16 18 20keVFull Scale 10124 cts Cursor: 0.000

Sum Spectrum

Spectrum processing : Peak possibly omitted : 4.501 keV

Processing option : All elements analyzed (Normalised)Number of iterations = 5

Standard :C CaCO3 1-Jun-1999 12:00 AMO SiO2 1-Jun-1999 12:00 AMMg MgO 1-Jun-1999 12:00 AMAl Al2O3 1-Jun-1999 12:00 AMSi SiO2 1-Jun-1999 12:00 AMS FeS2 1-Jun-1999 12:00 AMK MAD-10 Feldspar 1-Jun-1999 12:00 AMCa Wollastonite 1-Jun-1999 12:00 AMFe Fe 1-Jun-1999 12:00 AM

Elem... Weight% Atomic% C K 46.46 59.57O K 32.39 31.17Mg K 0.71 0.45Al K 1.69 0.96Si K 4.50 2.47S K 0.40 0.19K K 0.31 0.12Ca K 12.25 4.71Fe K 1.29 0.36

Totals 100.00

Ref. code: 25605722040416SAT

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6.6.3 Experiment on micro hardness

Vickers hardness test was performed in two concrete mixtures, which are

W40FM0 (containing fly ash having LOI of 0.77%) and W40 FM12 (containing fly

ash having LOI of 12.37%) at the age of 28 days. In this test the Vickers hardness was

not performed at the paste near to sand particles but near to the fly ash and carbon

particles. Moreover, the hardness values at different distances from the particles of fly

ash and carbon were also measured. It is quite difficult to measure the exact hardness

value around the carbon particles because fly ash particles were spreading all over the

surface of concrete and also near to carbon particles. Therefore, the tested points

around the carbon particles were selected by avoiding those fly ash particles. Also

measuring the hardness value of fly ash particles is a tough work, because the

majority of fly ash particles are very small, only the hardness values of fly ash

particles having large size can be measured.

For the mixture W40FM0, which contains 0.77% LOI fly ash, hardness values

around fly ash particles were recorded as shown in Table 6.1. For the mixtures

W40FM12, which contains 12% LOI fly ash, the hardness values around carbon and

fly ash particles were measured as listed in Tables 6.2 and 6.3, respectively. Figures

6.16 to 6.18 show the average hardness values and their tested locations around the

fly ash and carbon particles of mixtures W40FM0 and W40FM12.

The average hardness values near to carbon particles of W40FM12 mixture

were higher than those near to fly ash particles of both W40FM0 and W40FM12

mixtures. This result might be due to the water supplied from unburned carbon

particles, which causes additional hydration, producing shell like structure around the

carbon particles. The results of hardness values, measuring at different distances from

the particles of fly ash and carbon, demonstrate that the hardness values near to

carbon particles decreases as the distance from the carbon particles increases (see

Figure 6.17 comparing cases 5 and 5-1). On contrary, the hardness values near to fly

ash particles tend to increase as the distance from the fly ash particles increases (see

Figure 6.16 comparing cases 1 and 1-1, Figure 6.18 comparing cases 2 and 2-1). The

high hardness values near the carbon particles coincide with the hardness results of

bottom ash concrete studied by Hussain [64] which reports that the hardness values

near the bottom ash particles, which is a porous material, are higher than sand

particles due to the formation of a hard shell around its particles.

Ref. code: 25605722040416SAT

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Table 6.1 Hardness values near fly ash particles of W40FM0 mixture

Tested

Point No.

Vickers Hardness Value near particle

1 1-1 2 3 4 5

1 29.84 36.28 29.84 26.08 32.04 39.24

2 27.25 43.71 24.98 34.49 31.28 43.79

3 40.31 41.42 40.31 43.79 30.55 47.74

4 33.65 30.55 35.37 42.58 29.84 43.79

5 30.55 39.24 30.55 41.42 38.21 52.15

6 28.51 - 23.46 - 25.52 49.17

7 - - 27.87 - - 35.37

8 - - 49.17 - - -

9 - - 47.74 - - -

Avg 31.69 38.24 34.37 37.67 31.24 44.46

Figure 6.16 Average hardness values near to fly ash particles with their tested

locations of concrete containing fly ash with %LOI of 0.77%

Ref. code: 25605722040416SAT

90

Table 6.2 Hardness values near carbon particles of W40FM12 mixture

Tested

Point No.


1 2 3 4 5 5-1

1 75.71 52.25 52.25 57.43 69.96 41.42

2 59.33 50.68 53.89 55.63 53.89 42.5

3 53.89 52.25 75.71 53.89 71.65 45.05

4 55.62 - 67.95 54.47 53.89 47.95

5 69.96 - - - 61.32 -

6 59.33 - - - - -

7 55.62 - - - - -

Avg 61.35 51.73 62.45 55.36 62.14 44.23

Figure 6.17 Average hardness values near to carbon particles and their tested

locations of concrete containing fly ash with %LOI of 12%

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Table 6.3 Hardness values near fly ash particles of W40FM12 mixture

Tested

Point No.


1 2 2-1 2-2

1 29.17 63.42 46.36 39.24

2 43.79 55.62 47.74 29.84

3 - 39.24 - 35.37

4 - 27.87 - 29.26

5 - 31.28 - -

6 - 27.87 - -

7 - 40.31 - -

8 - 29.84 - -

9 - 45.05 - -

10 - 47.74 - -

Avg 36.48 40.82 47.05 33.43

Figure 6.18 Average hardness values near to fly ash particles and their tested

locations of concrete containing fly ash with %LOI of 12%

Ref. code: 25605722040416SAT

92

Chapter 7

Results of Durability of High LOI Fly Ash Concrete

7.1 Effect of high LOI fly ash on carbonation resistance

In this study, fly ashes with various %LOI were used to partially replace

cement at 20%, by weight. Carbonation depth of water-cured and air-cured concrete

specimens with water to binder ratios of 0.4 and 0.5 were measured. Specimens were

exposed in the accelerated carbonation environment for 28 and 56 days, respectively.

Figures 7.1 and 7.2 show the effect of high LOI fly ash on carbonation depth

of water-cured concrete, which were exposed for 28 and 56 days, respectively. At the

same water to binder ratio, it was found that carbonation depth of concrete gradually

increased along with the increase in %LOI of fly ash. The same tendencies were

obtained for both tested water to binder ratios of 0.4 and 0.5.

Using fly ash as a cement replacing material has been found to lower the

carbonation resistance of concrete due to the two main reasons: (1) fly ash delay the

hydration reaction and increase the porosity of concrete (2) the reduction in calcium

hydroxide(CH) by pozzolanic reaction of fly ash and by the reduced cement content.

Horiguchi et al [70], malami et al [72], and Sulapha et al [74] demonstrated a

significant relation between carbonation depth and porosity of concrete, in which

carbonation rate increased when the total pore volume increased. Roy et al [73] also

added that concrete having larger pores had higher carbonation rate than concrete that

had smaller pores. Therefore, in this case the higher carbonation depth of higher LOI

fly ash concrete might be the result of the higher total porosity of concrete.

As for the effect of curing, air-cured concrete exhibits higher carbonation

depth than the water-cured concrete (see Figures 7.2a and 7.2b), expressing the

inadequate curing of specimens in air-cured condition. The carbonation depths of air-

cured concrete increase along with the increase of %LOI of fly ash.

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(a) 28 days

(b) 56 days

Figure 7.1 Carbonation depth fly ash concrete containing various %LOI

at different exposure periods, (water-cured condition)

0

2

4

6

8

10

12

14

16

0 6 12 18 25

Car

bon

atio

n D

epth

(m

m)

LOI level, %

W40(WC)

W50(WC)

0

2

4

6

8

10

12

14

16

0 6 12 18 25

Car

bon

atio

n D

epth

(m

m)

LOI level, %

W40(WC)

W50(WC)

Ref. code: 25605722040416SAT

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(a) 28 days

(b) 56 days

Figure 7.2 Carbonation depth fly ash concrete containing various %LOI

at different exposure periods, (water-cured and air-cured conditions)

0

2

4

6

8

10

12

14

16

0 6 12 18 25

Car

bo

nat

ion D

epth

(m

m)

LOI level, %

W40(WC)

W50(WC)

W40(AC)

W50(AC)

0

2

4

6

8

10

12

14

16

0 6 12 18 25

Car

bon

atio

n D

epth

(m

m)

LOI level, %

W40(WC)

W50(WC)

W40(AC)

W50(AC)

Ref. code: 25605722040416SAT

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Curing sensitivity of high LOI fly ash concrete on carbonation at w/b of 0.4

was evaluated, in addition to the curing sensitivity based on compressive strength, by

using the curing sensitivity index ( CSICO2) which is the percentage difference

between carbonation depth of concrete that is water-cured and that of the air-cured

concrete as shown in equation (7.1). The higher curing sensitivity index means the

concrete is more sensitive to curing

%, CSICO2=

C𝑑(WC) − Cd(AC)

Cd(WC)× 100 (7.1)

where CSICO2is curing sensitivity index for carbonation (%). C𝑑(WC) and C𝑑(AC) are

carbonation depth of water-cured and air-cured specimens, respectively (mm).

Although the carbonation depth of concrete gradually increases with the

increase of %LOI of fly ash, high LOI fly ashes can reduce the curing sensitivity of

on carbonation (see Figure 7.3a). It can be seen that the CSICO2 based on carbonation

at 28 days of exposure had the similar tendency to that of CSIf𝑐′ based on compressive

strength (see Figures 6.9 and 6.10). The CSICO2 of fly ash concrete gradually

decreases from 49.46 to 35.65% when the %LOI of fly ash increases from 0.77%

(FM0) to 18.41% (FM18). Although the CSICO2 of fly ash having %LOI of

25.37%(FM25) starts to increase, Its CSICO2 is still lower than the fly ash with the

lowest LOI (LOI =0.77%). However, at longer exposure period, the ranges of %LOI

which allow high LOI fly ash concrete to perform better than low LOI fly ash were

smaller (see Figure 7.3b). In fact, fly ashes with LOI in the ranges of 0.77 to 18.41%

have similar CSICO2. A study by T.-H. Ha et al [14] demonstrated that the alkalinity of

fly ash mortar was greatly affected with the increase in carbon content, which may be

due to the reaction of carbon with the oxygen in the atmosphere thereby accelerating

the carbonation process. This might be another reason that the CSICO2of fly ash

concrete containing very high %LOI, which is generally known to contain with large

amount of unburned carbon particles, tends to greatly increase at longer exposure

period.

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(a) 28 days of exposure

(b) 56 days of exposure

Fig 7.3 Curing sensitivity index based on carbonation of fly ash concrete

containing various %LOI at different exposure periods, (w/b=0.4)

49.4645.59

38.2135.65

42.50

0

10

20

30

40

50

60

70

80


CS

I CO

2(%

)

MIX ID

43.7541.18

43.48 45.16

57.14

0

10

20

30

40

50

60

70

80


CS

I CO

2(%

)

MIX ID

Ref. code: 25605722040416SAT

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7.2 Effect of high LOI fly ash on chloride resistance

Chloride ion penetrability of OPC, low and high LOI fly ash concrete was

tested at water to binder ratios of 0.4 and 0.5. The charge passed results of OPC

mixture at 28, 56 and 91 days for water to binder ratio of 0.4 were 3945, 3366 and

3180, respectively and those for water to binder ratio of 0.5 were 7173, 6993 and

6879, respectively. Figures 7.4 and 7.5 show chloride ion penetrability of fly ash

concrete containing various %LOI at water to binder ratios of 0.4 and 0.5,

respectively. The overall results show that the charge passed values of fly ash

concrete with all %LOI level were lower than that of the OPC concrete at every tested

age. The lower chloride ion penetrability of concrete containing fly ash is related to

the refined pore structure and its reduced electrical conductivity [75]. However, when

comparing among the fly ash concrete, the charge passed values tend to increase with

the increase of %LOI of fly ash. The increase was smaller when the water to binder is

low (see Figure 7.4) but it could be clearly seen when w/b is high (see Figure 7.5).

The result indicates the poorer chloride resistance of higher %LOI fly ash mixtures

comparing to the lower LOI one. This result coincides with the total porosity results

in Chapter 6, which found that higher LOI of fly ash tends to increase total porosity of

the mortar and concrete, which therefore in this case lowers the chloride penetration

resistance of concrete. A study by T.-H. Ha et al [14] also found that the increase in

activated carbon content accelerated the corrosion of rebars in mortar containing fly

ash with different percentages of carbon.

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Figure 7.4 Chloride permissibility of fly ash concrete containing various %LOI

by measuring charge passed (w/b = 0.4)

Figure 7.5 Chloride permissibility of fly ash concrete containing various %LOI

by measuring charge passed (w/b = 0.5)

OPC 91 days

OPC 56 days

OPC 28 days

0

1000

2000

3000

4000

5000

6000

7000

8000

0 6 12 18 25

Char

ge

pas

s (c

oulo

mb

)

LOI of fly ash, %

28d

56d

91d

OPC 28 days

OPC 56 days

OPC 91 days

OPC 91 daysOPC 56 days

OPC 28 days

0

1000

2000

3000

4000

5000

6000

7000

8000

0 6 12 18 25

Char

ge

pas

s (c

oulo

mb

)

LOI of fly ash, %

28d

56d

91d

OPC 28 days

OPC 56 days

OPC 91 days

Ref. code: 25605722040416SAT

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7.3 Effect of high LOI fly ash on shrinkage

7.3.1 Autogenous shrinkage

Test results of autogenous shrinkage of paste specimens with water to binder

ratios of 0.25 and 0.40 are shown in Figures 7.6 and 7.7 respectively. It was found

that the use of fly ash with %LOI, ranging from 0.77 to 25%, reduces autogenous

shrinkage of concrete significantly comparing to the OPC concrete. Moreover, fly ash

with higher %LOI was even more effective to reduce the autogenous shrinkage than

the fly ash with low %LOI. This proves the internal curing ability of high LOI fly ash,

which is a porous material. A study by Hussain [64] found that the use of bottom ash,

which is also a porous material, significantly reduced autogenous shrinkage of

mortars and concrete due to its internal curing ability.

Figure 7.6 Autogenous shrinkage of pastes containing fly ashes with various %LOI

(w/b = 0.25)

-1000

-800

-600

-400

-200

0

0 4 8 12 21 35 49 63 77 91

Auto

gen

ous

shri

nkag

e (m

icro

n)

Age (days)

OPC FM0 FM6 FM12 FM18

Ref. code: 25605722040416SAT

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Figure 7.7 Autogenous shrinkage of pastes containing fly ashes with various %LOI

(w/b = 0.4)

7.3.2 Total shrinkage

The effect of high LOI fly ashes on total shrinkage is shown in Figures 7.8 and

7.9. It can be seen from these Figures that shrinkage of higher %LOI fly ash mixture

is higher than the mixtures that incorporate lower %LOI fly ash in both tested w/b of

0.4 and 0.5. The total shrinkage of paste gradually increases with the increase of

%LOI of fly ash. However, the use of fly ash with various %LOI (LOI=0.77 to 25%)

can reduce the total shrinkage when compared to the OPC mixture, since their total

shrinkages are still lower than that of the OPC mixture. But, it should be noted that fly

ash with very high %LOI could further increase the total shrinkage since it increase

the porosity of the concrete.

-1000

-800

-600

-400

-200

0

0 4 8 12 21 35 49 63 77 91A

uto

gen

ous

shri

nkag

e (m

icro

n)

Age (days)


Ref. code: 25605722040416SAT

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Figure 7.8 Total shrinkage of pastes containing fly ashes with various %LOI,

(w/b = 0.25)

Figure 7.9 Total shrinkage of pastes containing fly ashes with various %LOI,

(w/b = 0.4)

-2500

-2000

-1500

-1000

-500

0

0 4 8 12 21 35 49 63 77 91T

ota

l sh

rinkag

e (m

icro

n)

Age (days)


-2500

-2000

-1500

-1000

-500

0

0 4 8 12 21 35 49 63 77 91

To

tal sh

rinkag

e (m

icro

n)

Age (days)


Ref. code: 25605722040416SAT

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Chapter 8

Conclusions and Recommendations

8.1 Conclusions

This study examined the effects of high LOI fly ash on workability, compressive

strength and some durability properties of concrete by using artificial high LOI fly

ashes having various %LOI ranges from 0.77 to 25%. Based on all of the

experimental results in this study, the performances of high LOI fly ash mixtures

compared to low LOI fly ash mixtures having %LOI of 0.77% and cement-only

mixture are summarized and shown in Table 8.1 and Table 8.2, respectively.

Table 8.1 Performances of high LOI fly ash compared with low LOI fly ash

Test item Better Similar Worse

Workability

Water requirement

Initial slump


Early compressive strength*

Long-term compressive strength*

Durability


Total shrinkage**

Carbonation resistance

Chloride resistance (RCPT)**

Remark: *Better or similar depends on the level of %LOI of fly ash, the worse case

were only found in the case of controlled slump by adjustment of water.

**Performances are still better than those of cement-only mixtures.

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Table 8.2 Performances of high LOI fly ash mixture compared with cement-only

mixture

Test item Better Similar Worse

Workability

Water requirement*

Initial slump*


Early compressive strength

Long-term compressive strength*

Durability


Total shrinkage*

Carbonation resistance

Chloride resistance (RCPT)

Remark: *Better or similar or worse depends on the level of %LOI of fly ash

Apart from the performances of high LOI fly ash shown in Tables 8.1 and 8.2,

the results in the other aspects are additionally concluded as follows:

1. The moisture content of fly ash increases with the increase of its %LOI.

However, the moisture content of fly ash having %LOI of 25% is still lower than

the limit in ASTM standard specification, which limits the maximum moisture

content of fly ash used in concrete at 3%.

2. Particle size distributions of the prepared high LOI fly ashes are coarser than the

low LOI fly ash, whereas the Blaine fineness of high LOI fly ashes are higher.

This proves that high LOI fly ashes used in this study really have more porous

structure and contain irregular particles, because of the added PAC particles.

3. Water retainability of fly ash increases when %LOI of fly ash increases due to the

porous and rough-texture particles of the added PAC. Therefore, high LOI fly

ashes increase the water requirement of the mixtures.

4. Using low LOI fly ash significantly improves the slump of concrete compared to

the cement-only mixture. However, slump of fly ash concrete was significantly

affected by the %LOI of fly ash. The initial slump of concrete gradually

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decreases with the increase of %LOI of fly ash. Nevertheless, using fly ash

having %LOI of 0.77% to 6% with replacement percentage of 20% in the mixture

seems to improve the workability of concrete comparing to the cement-only

mixture.

5. Increase percent replacement of fly ash from 20% to 40% significantly enhances

slump of fly ash concrete having %LOI of 0 to 12%. On the contrary, the slump

of concrete with 40% fly ash replacement gradually decreases and becomes

worse than that of 20% replacement when %LOI of fly ash is over 12%. This

phenomenon is because when the high amount of fly ash, having very high %LOI

is used in the mixture, its water retainability plays the more important role than

its lubrication effect.

6. The reduction in compressive strength of high LOI fly ash concrete was obtained

in the case of the controlled slump by adjustment of water. However, the increase

in compressive strength of high LOI fly ash concrete was obtained in the cases of

the controlled slump by the use of superplasticizer and controlled w/b. In these 2

cases, the compressive strength of concrete gradually increases when %LOI of

fly ash increase from 0 to 12%. Although the compressive strength tends to

gradually decrease when %LOI of fly ash is beyond 12%, the overall

compressive strength of high LOI fly ash concrete is comparable to fly ash

concrete with the lowest %LOI (LOI=0.77%).

7. Increase the replacement percentage of fly ash from 20% to 40% resulted in

lower compressive strength for fly ash with all %LOI.

8. Using high LOI fly ashes in the mixtures can reduce the curing sensitivity of fly

ash concrete, especially the one that containing %LOI of 12% due to its internal

curing effect.

9. Although high LOI fly ashes increase porosity of concrete, the increase in

compressive strength of high LOI fly ash concrete was found to be due to its

internal curing effect. SEM pictures of polished high LOI fly ash concrete

showed that cement paste infiltrated into the rough surface and pores of the

carbon particles. Cement and fly ash might react with the additional water,

absorbed by the carbon particles, resulting in better bonding between cement and

carbon particles. Moreover, the result from micro hardness test of high LOI fly

ash concrete also revealed that the hardness values near to carbon particles were

Ref. code: 25605722040416SAT

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higher than those near to fly ash particles, proofing the existence of hard shell

around the carbon particles.

10. Carbonation and chloride resistance of high LOI fly ash concrete is worse than

the low LOI fly ash concrete. However, the effect of LOI of fly ash was less

significant when using in low w/b concrete.

11. Autogenous shrinkage of high LOI fly ash was significantly decreased. This

result is one of the evidences indicating the internal curinag ability of high LOI

fly ash.

12. Total shrinakge of high LOI fly ash was gradually increased with the increase of

%LOI of fly ash. However, the use of fly ash with %LOI of 0.77 to 25% can

reduce the total shrinkage when compared to the OPC mixture.

8.2 Recommendations for future studies

1. In this current study, the effect of high LOI fly ash has been carried out, by using

artificial high LOI fly ash produced from Mae-Moh fly ash. Mae-Moh fly ash is

low LOI fly ash but high in CaO content, which might be one of the reasons for

the strength gains of high LOI fly ash in this study. Therefore, the performances

of artificial high LOI fly ash produced from low CaO fly ash should be further

investigated.

2. The comparison between performances of artificial high LOI and real high LOI

fly ash should be further investigated.

Ref. code: 25605722040416SAT

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Appendices

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Appendix A

Physical properties of fine and coarse aggregates

Table A1 Physical properties of fine and coarse aggregates used in this study

Properties Fine aggregate Coarse aggregate

Bulk specific gravity (SSD) 2.59 2.83

Absorption (%) 1.16 0.34

Specific surface area, Ss (cm2/kg) 23429 1847

S/A minimum void (by volume) 0.43

Minimum void (%) 23.80

Fig A1 Sieve analysis result of fine aggregate

0

20

40

60

80

100

120

0.01 0.10 1.00 10.00 100.00

Cum

ula

tive

pas

sing (

%)

Sieve Size (mm)

Coarse limit fine limit River sand

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Fig B2 Sieve analysis result of coarse aggregate

0

10

20

30

40

50

60

70

80

90

100

1 10 100

% P

assi

ng

Sieve Size (mm)

Coarse limit Fine limit Crushed limestone

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Appendix B

An example of mix proportion calculation for making

artificial high LOI fly ashes

Table B.1 Chemical compositions of Mae-Moh fly ash and PAC-BC

Powder Loss on Ignition, %

Mae-Moh fly ash 0.77

PAC-BC 86.18

For example:

Need 20kg of artificial high LOI fly ash having %LOI of 18% (FM18).

%replacement of PAC = 18% − 0.77% = 17.23%

WPAC-BC = 20 kg × 17.23% = 3.446 kg

WFA = 20 kg – 3.446 kg = 16.554 kg

WPAC’-BC = 3.446 kg / 86.18% = 3.999 kg

Therefore, the mix proportion for FM18 is:

Mae-Moh fly ash = 16.554 kg

PAC-BC = 3.999 kg

Ref. code: 25605722040416SAT

effect of loi of fly ash on properties of...

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